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Quotient rule

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55178712
If \(h(x)=\frac{u(x)}{v(x)}\), where \(v(x)\ne0\), which formula is \(h'(x)\)? A) \(\frac{u'(x)}{v'(x)}\) B) \(\frac{u'(x)v(x)-u(x)v'(x)}{[v(x)]^2}\) C) \(\frac{u'(x)v(x)+u(x)v'(x)}{v(x)}\)

Hints

- The quotient-rule numerator contains a subtraction. - The denominator in the derivative is the square of the original denominator. - Dividing the two separate derivatives is not the quotient rule.

Solution

1. The quotient rule uses the derivative of the numerator times the denominator minus the numerator times the derivative of the denominator. 2. The entire numerator is divided by the square of the original denominator. 3. Therefore, formula B is correct.

Answer

B) \(\frac{u'(x)v(x)-u(x)v'(x)}{[v(x)]^2}\)
55178812
Suppose \(u(1)=6\), \(u'(1)=2\), \(v(1)=3\), and \(v'(1)=-1\). If \(h(x)=\frac{u(x)}{v(x)}\), find \(h'(1)\).

Hints

- Write the quotient rule symbolically before substituting the data. - Keep the subtraction in the numerator, especially because one supplied derivative value is negative. - Square the original denominator value, not its derivative.

Solution

1. By the quotient rule, \(h'(1)=\frac{u'(1)v(1)-u(1)v'(1)}{[v(1)]^2}\). 2. Substitute the values: \(h'(1)=\frac{2(3)-6(-1)}{3^2}=\frac{12}{9}=\frac{4}{3}\).

Answer

\(h'(1)=\frac{4}{3}\)
52732512
Find and simplify the derivative of \(f(x)=\frac{4x-1}{x^2+3}\).

Hints

- Use the quotient rule because both the numerator and denominator depend on \(x\). - Differentiate the numerator and denominator separately first. - Keep parentheses around complete numerator and denominator expressions when substituting. - Combine like terms in the resulting numerator.

Solution

1. Let \(u(x)=4x-1\) and \(v(x)=x^2+3\). Then \(u'(x)=4\) and \(v'(x)=2x\). 2. By the quotient rule, \(f'(x)=\frac{4(x^2+3)-(4x-1)(2x)}{(x^2+3)^2}\). 3. Simplify the numerator: \(4x^2+12-8x^2+2x=-4x^2+2x+12\). Therefore, \(f'(x)=\frac{-4x^2+2x+12}{(x^2+3)^2}\).

Answer

\(f'(x)=\frac{-4x^2+2x+12}{(x^2+3)^2}\)
52733012
Let \(f_k(x)=\frac{kx}{x^2+1}\), where \(k\in\mathbb{R}\). Find and simplify \(f_k'(x)\).

Hints

- Treat the parameter \(k\) as a constant. - Apply the quotient rule to the numerator and denominator. - Factor out the common factor \(k\) in the numerator.

Solution

1. Treat \(k\) as a constant. Let \(u(x)=kx\) and \(v(x)=x^2+1\). Then \(u'(x)=k\) and \(v'(x)=2x\). 2. By the quotient rule, \(f_k'(x)=\frac{k(x^2+1)-kx(2x)}{(x^2+1)^2}\). 3. Simplify and factor the numerator: \(k(x^2+1)-2kx^2=k(1-x^2)\). Therefore, \(f_k'(x)=\frac{k(1-x^2)}{(x^2+1)^2}\).

Answer

\(f_k'(x)=\frac{k(1-x^2)}{(x^2+1)^2}\)
52767112
Let \(f(x)=\frac{\ln x}{x}\). a) Find the maximal domain of \(f\). b) Use the quotient rule and write \(f'(x)\) before simplifying it. c) Simplify your derivative.

Hints

- Determine the logarithm's domain before differentiating. - For the Quotient Rule, identify the numerator and denominator and their derivatives. - Do not simplify the quotient-rule numerator until after part b.

Solution

1. The logarithm requires \(x>0\), which also keeps the denominator nonzero. Therefore, \(D_f=(0,\infty)\). 2. Applying the quotient rule gives \(f'(x)=\frac{(\frac1x)x-(\ln x)(1)}{x^2}\). 3. Simplifying gives \(f'(x)=\frac{1-\ln x}{x^2}\).

Answer

a) \(D_f=(0,\infty)\) b) \(f'(x)=\frac{(\frac1x)x-(\ln x)(1)}{x^2}\) c) \(f'(x)=\frac{1-\ln x}{x^2}\)
52790812
Find and simplify the derivative of \(h(x)=\frac{e^x+1}{e^x-1}\).

Hints

- Use the quotient rule. - Keep the subtraction and parentheses in the numerator. - Combine like exponential terms after expanding.

Solution

1. Let \(u(x)=e^x+1\) and \(v(x)=e^x-1\). Then \(u'(x)=e^x\) and \(v'(x)=e^x\). 2. By the quotient rule, \(h'(x)=\frac{e^x(e^x-1)-(e^x+1)e^x}{(e^x-1)^2}\). 3. The numerator simplifies to \(e^{2x}-e^x-e^{2x}-e^x=-2e^x\). Therefore, \(h'(x)=\frac{-2e^x}{(e^x-1)^2}\), for \(x\ne 0\).

Answer

\(h'(x)=\frac{-2e^x}{(e^x-1)^2}\), for \(x\ne 0\)
52948212
Consider \(h(x)=\frac{x^3-5x+2}{8}\). 1) Find \(h'(x)\) using the quotient rule. 2) Rewrite the function so that you can use the constant-multiple rule, and differentiate again. 3) Explain why the constant-multiple rule is more efficient here.

Hints

- The derivative of a constant denominator is zero. - Rewrite division by \(8\) as multiplication by \(\frac{1}{8}\). - Compare the number of algebraic steps in the two methods. - Notice which quotient-rule term vanishes.

Solution

1. Using the quotient rule with constant denominator \(8\), \(h'(x)=\frac{(3x^2-5)\cdot 8-(x^3-5x+2)\cdot 0}{8^2}\) \(=\frac{3x^2-5}{8}\). 2. Rewrite the function as \(h(x)=\frac{1}{8}(x^3-5x+2)\). Then \(h'(x)=\frac{1}{8}(3x^2-5)\). 3. The constant-multiple rule avoids squaring the denominator and then canceling the same constant factor.

Answer

1) \(h'(x)=\frac{3x^2-5}{8}\) 2) \(h(x)=\frac{1}{8}(x^3-5x+2)\), so \(h'(x)=\frac{1}{8}(3x^2-5)\). 3) The constant-multiple rule requires fewer algebraic steps.
52948412
Consider \(g(x)=\frac{2x^3+x^2+1}{x^2}\), where \(x\ne 0\). Find \(g'(x)\) in two ways. a) Divide each numerator term by \(x^2\), and then differentiate the resulting sum. b) Apply the quotient rule to the original expression. Compare the amount of work required. Which method is more efficient?

Hints

- Divide each numerator term separately by the denominator. - A sum of powers is usually easier to differentiate than a quotient. - Track the negative exponent when differentiating \(x^{-2}\). - Simplify the quotient-rule result by factoring and canceling.

Solution

1. For a), divide term by term: \(g(x)=2x+1+x^{-2}\). Therefore, \(g'(x)=2-2x^{-3}=2-\frac{2}{x^3}\). 2. For b), use the quotient rule: \(g'(x)=\frac{(6x^2+2x)x^2-(2x^3+x^2+1)(2x)}{x^4}\) \(=\frac{2x^4-2x}{x^4}\) \(=2-\frac{2}{x^3}\). 3. Dividing term by term is more efficient because it reduces the problem to the power rule and avoids the longer quotient-rule simplification.

Answer

a) \(g'(x)=2-\frac{2}{x^3}\) b) The quotient rule gives the same derivative. Term-by-term division is more efficient.
52948712
Use the quotient rule to find the derivative of \(f(x)=\frac{\sin(x)}{x^2+3}\).

Hints

- Identify the numerator and denominator functions. - Recall the derivatives of sine and a quadratic polynomial. - Apply the quotient rule. - Leave the denominator as a square.

Solution

1. Let \(u(x)=\sin(x)\) and \(v(x)=x^2+3\). Then \(u'(x)=\cos(x)\) and \(v'(x)=2x\). 2. By the quotient rule, \(f'(x)=\frac{\cos(x)(x^2+3)-\sin(x)(2x)}{(x^2+3)^2}\). Therefore, \(f'(x)=\frac{(x^2+3)\cos(x)-2x\sin(x)}{(x^2+3)^2}\).

Answer

\(f'(x)=\frac{(x^2+3)\cos(x)-2x\sin(x)}{(x^2+3)^2}\)
52948912
Find the derivative of \(f(x)=\frac{0.5x^2+4x-1}{2x+3}\). Simplify the numerator as much as possible.

Hints

- Use the quotient rule. - Differentiate the numerator and denominator separately first. - Keep the second product in parentheses because it is subtracted. - Leave the denominator as a square.

Solution

1. Let \(u(x)=0.5x^2+4x-1\) and \(v(x)=2x+3\). Then \(u'(x)=x+4\) and \(v'(x)=2\). 2. By the quotient rule, \(f'(x)=\frac{(x+4)(2x+3)-2(0.5x^2+4x-1)}{(2x+3)^2}\). 3. Simplify the numerator: \((2x^2+11x+12)-(x^2+8x-2)=x^2+3x+14\). Therefore, \(f'(x)=\frac{x^2+3x+14}{(2x+3)^2}\).

Answer

\(f'(x)=\frac{x^2+3x+14}{(2x+3)^2}\)
52949012
Let \(h(x)=\frac{x^4-2}{x^2+x}\). Use the quotient rule to find \(h'(x)\), and state the domain of the derivative.

Hints

- Use the quotient rule. - Write the numerator function, denominator function, and their derivatives before substituting. - Keep parentheses around the second product in the numerator. - Factor the original denominator to identify excluded values.

Solution

1. Let \(u(x)=x^4-2\) and \(v(x)=x^2+x\). Then \(u'(x)=4x^3\) and \(v'(x)=2x+1\). 2. By the quotient rule, \(h'(x)=\frac{4x^3(x^2+x)-(x^4-2)(2x+1)}{(x^2+x)^2}\). 3. Expand and combine like terms in the numerator: \(4x^5+4x^4-(2x^5+x^4-4x-2)=2x^5+3x^4+4x+2\). Therefore, \(h'(x)=\frac{2x^5+3x^4+4x+2}{(x^2+x)^2}\). The derivative is defined for \(x\ne 0\) and \(x\ne -1\).

Answer

\(h'(x)=\frac{2x^5+3x^4+4x+2}{(x^2+x)^2}\), with \(x\ne 0\) and \(x\ne -1\)
52949612
Use the quotient rule to find the derivative of \(f(x)=\frac{x+5}{x^3}\). Simplify your result as much as possible.

Hints

- Use the quotient rule. - Differentiate the numerator and denominator separately. - Factor the numerator after applying the rule. - Cancel only factors, not individual terms.

Solution

1. Let \(u(x)=x+5\) and \(v(x)=x^3\). Then \(u'(x)=1\) and \(v'(x)=3x^2\). 2. By the quotient rule, \(f'(x)=\frac{x^3-3x^2(x+5)}{x^6}\). 3. Simplify and cancel a common factor of \(x^2\): \(f'(x)=\frac{-2x^3-15x^2}{x^6}=\frac{-2x-15}{x^4}\), where \(x\ne 0\).

Answer

\(f'(x)=\frac{-2x-15}{x^4}\), with \(x\ne 0\)
52954412
For \(t\in\mathbb{R}\setminus\{0\}\), consider the family of functions \(f_t(x)=\frac{tx^2}{x+t}\). Find \(f_t'(x)\), treating \(t\) as a constant, and state the domain.

Hints

- Use the quotient rule. - Treat the parameter \(t\) as a constant when differentiating with respect to \(x\). - Combine like terms in the numerator before factoring. - Find the excluded input from the original denominator.

Solution

1. Let \(u(x)=tx^2\) and \(v(x)=x+t\). Treating \(t\) as a constant gives \(u'(x)=2tx\) and \(v'(x)=1\). 2. By the quotient rule, \(f_t'(x)=\frac{2tx(x+t)-tx^2}{(x+t)^2}\). 3. Simplify and factor the numerator: \(2tx^2+2t^2x-tx^2=tx^2+2t^2x=tx(x+2t)\). Thus, \(f_t'(x)=\frac{tx(x+2t)}{(x+t)^2}\), with \(x\ne -t\).

Answer

\(f_t'(x)=\frac{tx(x+2t)}{(x+t)^2}\), with \(x\ne -t\)
53451712
Consider the family of functions \(g_a(x)=\frac{a-x}{ax+1}\), where \(a\in\mathbb{R}\setminus\{0\}\). Find the slope at \(x=0\) in terms of \(a\).

Hints

- Treat \(a\) as a constant while differentiating with respect to \(x\). - Apply the quotient rule before evaluating at \(x=0\). - Simplify the quotient-rule numerator carefully because several parameter terms cancel.

Solution

1. Using the quotient rule, \(g_a'(x)=\frac{-(ax+1)-a(a-x)}{(ax+1)^2}\). 2. The numerator simplifies to \(-(1+a^2)\), so \(g_a'(x)=-\frac{1+a^2}{(ax+1)^2}\). 3. At \(x=0\), the slope is \(g_a'(0)=-(1+a^2)\).

Answer

\(g_a'(0)=-(1+a^2)\)
55603812
The table gives values of differentiable functions \(f\) and \(g\) and their derivatives at \(x=-1\). <table><tr><th>Function</th><th>Value at \(-1\)</th><th>Derivative at \(-1\)</th></tr><tr><td>\(f\)</td><td>\(6\)</td><td>\(-2\)</td></tr><tr><td>\(g\)</td><td>\(3\)</td><td>\(4\)</td></tr></table> Let \(q(x)=\frac{f(x)}{g(x)}\). Find \(q'(-1)\).

Hints

- Keep the numerator order of the Quotient Rule consistent before using the table. - The denominator uses the square of the denominator function's value, not its derivative. - Substitute the four table entries only after writing the complete rule.

Solution

1. Use the Quotient Rule: \(q'(x)=\frac{f'(x)g(x)-f(x)g'(x)}{[g(x)]^2}\). 2. Substitute the table values at \(x=-1\): \(q'(-1)=\frac{(-2)(3)-6(4)}{3^2}=\frac{-30}{9}=-\frac{10}{3}\).

Answer

\(q'(-1)=-\frac{10}{3}\)
52598712
Let \(f(x)=\frac{x^2-4}{x^2+4}\). a) Find the x-intercepts of the graph. b) Find equations of the tangent lines at those intercepts. c) The tangent lines intersect at \(S\). Find \(S\) and the area of the triangle bounded by the two tangent lines and the x-axis.

Hints

- A rational function is zero when its numerator is zero and its denominator is not. - Use the quotient rule to find the derivative. - A tangent line requires a point and a slope. - Use the intercepts as the triangle's base and the tangent intersection to find its height.

Solution

1. The numerator is zero at \(x=-2\) and \(x=2\), while the denominator is nonzero. The x-intercepts are \((-2,0)\) and \((2,0)\). 2. Differentiate using the quotient rule: \(f'(x)=\frac{2x(x^2+4)-(x^2-4)(2x)}{(x^2+4)^2}=\frac{16x}{(x^2+4)^2}\). 3. The slopes are \(f'(-2)=-\frac{1}{2}\) and \(f'(2)=\frac{1}{2}\). 4. The tangent lines are \(y=-\frac{1}{2}(x+2)=-\frac{1}{2}x-1\) and \(y=\frac{1}{2}(x-2)=\frac{1}{2}x-1\). 5. Set the line equations equal. This gives \(x=0\) and \(y=-1\), so \(S=(0,-1)\). 6. The base on the x-axis has length \(4\), and the height is \(1\). Therefore, the area is \(\frac{1}{2}\cdot 4\cdot 1=2\).

Answer

a) \((-2,0)\) and \((2,0)\) b) \(y=-\frac{1}{2}x-1\) and \(y=\frac{1}{2}x-1\) c) \(S=(0,-1)\); area \(=2\) square units
52732612
Find a fully simplified expression for the derivative of \(f(x)=\frac{x^2+1}{(2x-1)^2}\).

Hints

- Expand the squared denominator before differentiating so the quotient rule is the only new rule needed. - Keep the subtraction in the quotient-rule numerator grouped until both products are complete. - Factor the final expression to expose any cancellation.

Solution

1. Expand the denominator before differentiating: \((2x-1)^2=4x^2-4x+1\). 2. Let \(u(x)=x^2+1\) and \(v(x)=4x^2-4x+1\). Then \(u'(x)=2x\) and \(v'(x)=8x-4\). 3. Apply the quotient rule: \(f'(x)=\frac{2x(4x^2-4x+1)-(x^2+1)(8x-4)}{(4x^2-4x+1)^2}\). 4. Simplifying and factoring gives \(f'(x)=\frac{-2(x+2)}{(2x-1)^3}\).

Answer

\(f'(x)=\frac{-2(x+2)}{(2x-1)^3}\)
52732912
Use the quotient rule to find the derivative of each function. Simplify each numerator. a) \(f(x)=\frac{5}{x^2+1}\) b) \(f(x)=\frac{x}{x-3}\) c) \(f(x)=\frac{x^2+4}{x}\) d) \(f(x)=\frac{2x-1}{x^2+2}\)

Hints

- Identify the numerator and denominator functions first. - Differentiate those two functions before substituting into the quotient rule. - Track the negative sign before the second product in the quotient-rule numerator. - Usually the denominator can remain as a square.

Solution

1. For a), \(f'(x)=\frac{0(x^2+1)-5(2x)}{(x^2+1)^2}=\frac{-10x}{(x^2+1)^2}\). 2. For b), \(f'(x)=\frac{1(x-3)-x(1)}{(x-3)^2}=\frac{-3}{(x-3)^2}\). 3. For c), \(f'(x)=\frac{2x(x)-(x^2+4)(1)}{x^2}=\frac{x^2-4}{x^2}\). 4. For d), \(f'(x)=\frac{2(x^2+2)-(2x-1)(2x)}{(x^2+2)^2}\) \(=\frac{-2x^2+2x+4}{(x^2+2)^2}\).

Answer

a) \(f'(x)=\frac{-10x}{(x^2+1)^2}\) b) \(f'(x)=\frac{-3}{(x-3)^2}\) c) \(f'(x)=\frac{x^2-4}{x^2}\) d) \(f'(x)=\frac{-2x^2+2x+4}{(x^2+2)^2}\)
52733412
Let \(f(x)=\frac{3}{x^4}+\frac{x^2}{2x-1}\), where \(x\ne 0\) and \(x\ne 0.5\). Find \(f'(x)\). Use the power rule with a negative exponent for the first term and the quotient rule for the second term. Simplify the result.

Hints

- Differentiate the two terms separately. - Rewrite the first denominator using a negative exponent. - Use the quotient rule for the second term. - Expand and combine the quotient-rule numerator carefully.

Solution

1. Rewrite the first term as \(3x^{-4}\). Its derivative is \(-12x^{-5}=-\frac{12}{x^5}\). 2. For the second term, let \(u(x)=x^2\) and \(v(x)=2x-1\). By the quotient rule, \(\left(\frac{x^2}{2x-1}\right)'=\frac{2x(2x-1)-x^2\cdot 2}{(2x-1)^2}\). 3. Simplify the numerator: \(2x(2x-1)-2x^2=2x^2-2x=2x(x-1)\). Therefore, \(f'(x)=-\frac{12}{x^5}+\frac{2x(x-1)}{(2x-1)^2}\).

Answer

\(f'(x)=-\frac{12}{x^5}+\frac{2x(x-1)}{(2x-1)^2}\)
52733512
Errors were made while finding the derivatives of \(f\) and \(g\). 1) \(f(x)=\frac{x^2}{2x-3}\), with the incorrect result \(f'(x)=\frac{2x(2x-3)-x^2\cdot 2}{2x-3}\) 2) \(g(x)=\frac{3x-1}{x^2+5}\), with the incorrect result \(g'(x)=\frac{3(x^2+5)+(3x-1)(2x)}{(x^2+5)^2}\) Describe each error and give the correct simplified derivative.

Hints

- Compare each calculation with the quotient rule. - Check the structure of the denominator. - Check the operation between the two products in the numerator. - Distribute a negative sign carefully when simplifying.

Solution

1. For \(f\), the denominator in the quotient rule must be squared. The correct derivative is \(f'(x)=\frac{2x(2x-3)-2x^2}{(2x-3)^2}\) \(=\frac{2x^2-6x}{(2x-3)^2}\). 2. For \(g\), the quotient-rule numerator requires subtraction, not addition. The correct derivative is \(g'(x)=\frac{3(x^2+5)-(3x-1)(2x)}{(x^2+5)^2}\) \(=\frac{-3x^2+2x+15}{(x^2+5)^2}\).

Answer

1) Error: The denominator was not squared. \(f'(x)=\frac{2x^2-6x}{(2x-3)^2}\) 2) Error: The two products in the numerator were added instead of subtracted. \(g'(x)=\frac{-3x^2+2x+15}{(x^2+5)^2}\)
52733612
Let \(f(x)=\frac{x^2-8}{x-3}\). a) Use the quotient rule to find and simplify \(f'(x)\). b) Find every point where the graph of \(f\) has a horizontal tangent.

Hints

- A horizontal tangent has slope zero. - A rational expression is zero when its numerator is zero and its denominator is nonzero. - Check that every solution is in the domain of the original function.

Solution

1. Let \(u(x)=x^2-8\) and \(v(x)=x-3\). Then \(u'(x)=2x\) and \(v'(x)=1\). 2. By the quotient rule, \(f'(x)=\frac{2x(x-3)-(x^2-8)}{(x-3)^2}\) \(=\frac{x^2-6x+8}{(x-3)^2}\). 3. A horizontal tangent occurs where \(f'(x)=0\). Since the denominator is nonzero in the domain, solve \(x^2-6x+8=0\). Factoring gives \((x-2)(x-4)=0\), so \(x=2\) or \(x=4\). Both values are in the domain. 4. Evaluate the function at those inputs: \(f(2)=4\) and \(f(4)=8\). Therefore, the horizontal tangent points are \((2,4)\) and \((4,8)\).

Answer

a) \(f'(x)=\frac{x^2-6x+8}{(x-3)^2}\) b) The horizontal tangent points are \((2,4)\) and \((4,8)\).
52733912
Let \(f(x)=\frac{x^2}{x+2}\). Find the coordinates of every point on the graph of \(f\) where the tangent has slope \(m=0.75\).

Hints

- The derivative gives the tangent slope. - Use the quotient rule to find the derivative. - Set the derivative equal to the given slope. - Substitute each resulting \(x\)-value into the original function to find the point.

Solution

1. By the quotient rule, \(f'(x)=\frac{2x(x+2)-x^2}{(x+2)^2}=\frac{x^2+4x}{(x+2)^2}\). 2. Set the derivative equal to the desired slope: \(\frac{x^2+4x}{(x+2)^2}=\frac{3}{4}\). 3. Cross-multiply and simplify: \(4(x^2+4x)=3(x^2+4x+4)\), so \(x^2+4x-12=0\). Factoring gives \(x=2\) or \(x=-6\). 4. Find the corresponding function values: \(f(2)=1\) and \(f(-6)=-9\). Therefore, the points are \((2,1)\) and \((-6,-9)\).

Answer

The points are \((2,1)\) and \((-6,-9)\).
52734012
Let \(f(x)=\frac{2x+2}{x-2}\). Find the coordinates of every point where the graph of \(f\) has slope \(m=-1.5\).

Hints

- The derivative gives the slope of the graph. - Apply the quotient rule. - Exclude any value that makes the original denominator zero. - Substitute each solution into the original function to find the full coordinates.

Solution

1. By the quotient rule, \(f'(x)=\frac{2(x-2)-(2x+2)}{(x-2)^2}=\frac{-6}{(x-2)^2}\). 2. Set the derivative equal to the given slope: \(\frac{-6}{(x-2)^2}=-1.5\). Thus, \((x-2)^2=4\), so \(x=4\) or \(x=0\). 3. Evaluate the original function: \(f(4)=5\) and \(f(0)=-1\). Therefore, the points are \((4,5)\) and \((0,-1)\).

Answer

The points are \((4,5)\) and \((0,-1)\).
52734112
Let \(f(x)=\frac{x+2}{x^2+1}\). Find the equation of the tangent line to the graph of \(f\) at \(x_0=1\).

Hints

- A tangent line requires a point and a slope. - The function value gives the point, and the derivative gives the slope. - Use the quotient rule to find the derivative. - Apply point-slope form.

Solution

1. Find the point on the graph: \(f(1)=\frac{3}{2}=1.5\). 2. By the quotient rule, \(f'(x)=\frac{(x^2+1)-(x+2)(2x)}{(x^2+1)^2}\) \(=\frac{-x^2-4x+1}{(x^2+1)^2}\). 3. The tangent slope is \(f'(1)=\frac{-1-4+1}{4}=-1\). 4. Use point-slope form through \((1,1.5)\): \(y-1.5=-(x-1)\), so \(y=-x+2.5\).

Answer

The tangent line is \(y=-x+2.5\).
52734712
For each part, determine whether \(g(x)\) is the derivative of \(f(x)\). a) \(f(x)=\frac{x^2+2}{0.4x^2-1}\), \(g(x)=\frac{-3.6x}{(0.4x^2-1)^2}\) b) \(f(x)=4x^{-2}+\frac{1}{x}\), \(g(x)=\frac{x+8}{x^3}\)

Hints

- Apply the quotient rule in part a. - In part b, either combine the terms or differentiate the negative powers directly. - Track the subtraction in the quotient-rule numerator. - Compare the signs of the final numerators carefully.

Solution

1. For a), apply the quotient rule: \(f'(x)=\frac{2x(0.4x^2-1)-(x^2+2)(0.8x)}{(0.4x^2-1)^2}\). The numerator simplifies to \(0.8x^3-2x-0.8x^3-1.6x=-3.6x\). Therefore, \(f'(x)=\frac{-3.6x}{(0.4x^2-1)^2}=g(x)\). 2. For b), use the power rule: \(f'(x)=-8x^{-3}-x^{-2}\) \(=\frac{-8-x}{x^3}\). This is the negative of the proposed numerator, so \(g\) is not the derivative of \(f\).

Answer

a) Yes. \(g(x)=f'(x)\). b) No. The correct derivative is \(f'(x)=\frac{-x-8}{x^3}\).
52735312
Let \(f(x)=\frac{x^2}{x-1}\), with domain \(\mathbb{R}\setminus\{1\}\). Jordan claims that the graph has horizontal tangents at \(x=0\) and \(x=2\). Maya claims that \(x=2\) is the only such value. Use the Quotient Rule on the original quotient to compute \(f'(x)\). Do not rewrite \(f\) by polynomial division. Then decide whose claim is complete and justify your conclusion.

Hints

- Keep the numerator and denominator roles separate when applying the Quotient Rule. - Simplify the derivative only after the Quotient Rule has been set up correctly. - For a rational derivative, determine when its numerator can be zero while its denominator remains defined.

Solution

1. Apply the Quotient Rule to the original quotient: \(f'(x)=\frac{2x(x-1)-x^2}{(x-1)^2}\). 2. Simplify the numerator: \(2x(x-1)-x^2=x^2-2x=x(x-2)\). Therefore, \(f'(x)=\frac{x(x-2)}{(x-1)^2}\). 3. A horizontal tangent requires \(f'(x)=0\). Since \(x=1\) is excluded from the domain and the denominator is nonzero elsewhere, set the numerator equal to zero: \(x(x-2)=0\). Thus, \(x=0\) or \(x=2\). 4. Jordan's claim is complete. Maya omitted \(x=0\).

Answer

\(f'(x)=\frac{x(x-2)}{(x-1)^2}\). The horizontal tangents occur at \(x=0\) and \(x=2\), so Jordan's claim is complete and Maya's is not.
52735412
Find every \(x\)-value where \(g(x) = \frac{x^2 - 4}{x^2 + 1}\) has a horizontal tangent. A student claims, “Because the numerator is zero at \(x = 2\) and \(x = -2\), the graph must have horizontal tangents there.” Evaluate the claim by checking the derivative.

Hints

- What derivative condition defines a horizontal tangent? - Distinguish between zeros of a function and zeros of its derivative. - Use the quotient rule to find the slope function. - When is a rational expression equal to zero?

Solution

1. Apply the quotient rule: \(g'(x) = \frac{2x(x^2 + 1) - 2x(x^2 - 4)}{(x^2 + 1)^2}\). 2. Simplify: \(g'(x) = \frac{10x}{(x^2 + 1)^2}\). 3. A horizontal tangent occurs where \(g'(x) = 0\). Since the denominator is always positive, solve \(10x = 0\), which gives \(x = 0\). 4. The student confused zeros of the function with zeros of its derivative. At \(x = 2\), \(g'(2) = \frac{4}{5}\), and at \(x = -2\), \(g'(-2) = -\frac{4}{5}\), so neither tangent is horizontal.

Answer

The claim is false. The only horizontal tangent occurs at \(x = 0\). The values \(x = \pm 2\) are zeros of \(g\), not zeros of \(g'\).
52736912
Consider the family \(f_a(x)=\frac{ax}{x^2+x+1}\), where \(a\ne0\). Show algebraically that the x-coordinates of the local extrema are the same for every value of \(a\). Method requirement: For every conclusion that a local extremum occurs, show the sign of the relevant first derivative on the two sides of the critical number and explicitly use the first derivative test. A critical-number calculation alone is not sufficient.

Hints

- Apply the quotient rule. - Determine which factors can equal zero. - Check that the derivative changes sign at the solutions.

Solution

1. The quotient rule gives \(f_a'(x)=a\frac{1-x^2}{(x^2+x+1)^2}\). 2. The denominator is positive for every real \(x\), and \(a\ne0\). Therefore, \(f_a'(x)=0\) exactly when \(1-x^2=0\). 3. The solutions are \(x=-1\) and \(x=1\). The numerator changes sign at both values, so both are local-extremum x-coordinates for every \(a\).

Answer

\(x=-1\) and \(x=1\)
52738912
Let \(f(x)=\frac{x^2-3}{x^2+1}\). A student writes \(f'(x)=\frac{2x(x^2+1)-(x^2-3)}{(x^2+1)^2}\). Identify the Quotient Rule error, compute \(f'(x)\) correctly from the original quotient, and find the value of \(x\) where the graph has a horizontal tangent.

Hints

- Identify the numerator and denominator functions and their derivatives before comparing the student's expression with the Quotient Rule. - Check both products in the derivative numerator; each must contain the appropriate derivative factor. - After correcting the derivative, use the fact that the denominator is always positive to locate a zero of the derivative.

Solution

1. The denominator is \(x^2+1\), whose derivative is \(2x\). In the Quotient Rule numerator, the second product must therefore include this factor. The student omitted it. 2. Apply the Quotient Rule correctly: \(f'(x)=\frac{2x(x^2+1)-(x^2-3)(2x)}{(x^2+1)^2}\). 3. Simplify the numerator: \(2x[(x^2+1)-(x^2-3)]=2x(4)=8x\). Thus, \(f'(x)=\frac{8x}{(x^2+1)^2}\). 4. Since \((x^2+1)^2>0\) for every real \(x\), the derivative is zero exactly when \(8x=0\). Hence the graph has a horizontal tangent at \(x=0\).

Answer

The student omitted the derivative factor \(2x\) from the second product in the Quotient Rule numerator. The correct derivative is \(f'(x)=\frac{8x}{(x^2+1)^2}\), so the horizontal tangent occurs at \(x=0\).
52739012
Consider \(f(x)=\frac{x+2}{e^{0.5x}}\). a) Use the quotient rule to find \(f'(x)\). b) Rewrite \(f(x)=(x+2)e^{-0.5x}\), and use the product rule and chain rule to obtain the same derivative. c) Find the x-coordinate where the graph has a horizontal tangent.

Hints

- Apply the quotient rule carefully. - Rewriting the denominator as a negative exponent turns the quotient into a product. - Use the chain rule for \(e^{ax}\). - A horizontal tangent occurs where the derivative is zero.

Solution

1. For the quotient-rule method, let \(u(x)=x+2\) and \(v(x)=e^{0.5x}\). Then \(u'(x)=1\) and \(v'(x)=0.5e^{0.5x}\). Thus, \(f'(x)=\frac{e^{0.5x}-0.5(x+2)e^{0.5x}}{e^x}\) \(=-0.5x e^{-0.5x}\). 2. For the product-rule method, \(f'(x)=e^{-0.5x}+(x+2)(-0.5e^{-0.5x})\) \(=-0.5x e^{-0.5x}\). 3. A horizontal tangent occurs where \(-0.5x e^{-0.5x}=0\). Since the exponential factor is never zero, \(x=0\).

Answer

a) \(f'(x)=-0.5x e^{-0.5x}\) b) The product-rule method gives the same expression. c) The horizontal tangent occurs at \(x=0\).
52739512
Find the derivative of \(f(x)=4x^2+\frac{e^x}{x+3}\).

Hints

- Differentiate the two terms separately. - Use the quotient rule for the exponential fraction. - Factor out the common exponential factor in the quotient-rule numerator.

Solution

1. Differentiate the polynomial term: \(\frac{d}{dx}(4x^2)=8x\). 2. For the quotient, let \(u(x)=e^x\) and \(v(x)=x+3\). Then \(u'(x)=e^x\) and \(v'(x)=1\). 3. By the quotient rule, \(\frac{d}{dx}\left(\frac{e^x}{x+3}\right)=\frac{e^x(x+3)-e^x}{(x+3)^2}\) \(=\frac{(x+2)e^x}{(x+3)^2}\). Therefore, \(f'(x)=8x+\frac{(x+2)e^x}{(x+3)^2}\).

Answer

\(f'(x)=8x+\frac{(x+2)e^x}{(x+3)^2}\)
52739612
Find the derivative of \(f(t)=\frac{t\sin(t)}{t-1}\).

Hints

- Use the quotient rule for the overall expression. - The numerator requires the product rule. - Expand the quotient-rule numerator carefully. - Look for terms that cancel.

Solution

1. Let \(u(t)=t\sin(t)\) and \(v(t)=t-1\). 2. Use the product rule on the numerator: \(u'(t)=\sin(t)+t\cos(t)\). Also, \(v'(t)=1\). 3. By the quotient rule, \(f'(t)=\frac{[\sin(t)+t\cos(t)](t-1)-t\sin(t)}{(t-1)^2}\). 4. Expand and combine terms in the numerator: \(t\sin(t)-\sin(t)+t^2\cos(t)-t\cos(t)-t\sin(t)\) \(=(t^2-t)\cos(t)-\sin(t)\). Therefore, \(f'(t)=\frac{(t^2-t)\cos(t)-\sin(t)}{(t-1)^2}\).

Answer

\(f'(t)=\frac{(t^2-t)\cos(t)-\sin(t)}{(t-1)^2}\)
52740712
Let \(f(x)=\frac{(x^2-1)^2}{x^2+3}\). a) Use the quotient rule and chain rule to find \(f'(x)\). Factor the numerator as completely as possible. b) Find every value of \(x\) where the graph of \(f\) has a horizontal tangent.

Hints

- Use the quotient rule for the overall function and the chain rule for the squared numerator. - Factor the derivative numerator instead of expanding it completely. - A horizontal tangent occurs where the derivative is zero. - A fraction is zero when its numerator is zero and its denominator is nonzero.

Solution

1. Let \(u(x)=(x^2-1)^2\) and \(v(x)=x^2+3\). By the chain rule, \(u'(x)=4x(x^2-1)\), and \(v'(x)=2x\). 2. Apply the quotient rule: \(f'(x)=\frac{4x(x^2-1)(x^2+3)-(x^2-1)^2(2x)}{(x^2+3)^2}\). 3. Factor \(2x(x^2-1)\) from the numerator: \(f'(x)=\frac{2x(x^2-1)[2(x^2+3)-(x^2-1)]}{(x^2+3)^2}\) \(=\frac{2x(x^2-1)(x^2+7)}{(x^2+3)^2}\). 4. A horizontal tangent occurs where the numerator is zero: \(2x(x^2-1)(x^2+7)=0\). Since \(x^2+7>0\), the real solutions are \(x=-1\), \(x=0\), and \(x=1\).

Answer

a) \(f'(x)=\frac{2x(x^2-1)(x^2+7)}{(x^2+3)^2}\) b) The horizontal tangents occur at \(x=-1\), \(x=0\), and \(x=1\).
52741912
Find and simplify the derivative of each function. a) \(f(x)=\frac{x^2-9}{3x+2}\) b) \(g(t)=\frac{e^t}{t^2+1}\)

Hints

- Apply the quotient rule in each part. - Use the basic derivative of \(e^t\) in part b. - Factor the completed numerator before deciding that the expression is simplified.

Solution

1. For part a, the quotient rule gives \(f'(x)=\frac{2x(3x+2)-3(x^2-9)}{(3x+2)^2}=\frac{3x^2+4x+27}{(3x+2)^2}\). 2. For part b, the quotient rule gives \(g'(t)=\frac{e^t(t^2+1)-e^t(2t)}{(t^2+1)^2}\). 3. Factor the numerator: \(g'(t)=\frac{e^t(t^2-2t+1)}{(t^2+1)^2}=\frac{e^t(t-1)^2}{(t^2+1)^2}\).

Answer

a) \(f'(x)=\frac{3x^2+4x+27}{(3x+2)^2}\) b) \(g'(t)=\frac{e^t(t-1)^2}{(t^2+1)^2}\)
52742012
Find and simplify the derivative of each function. a) \(f(x)=\frac{1}{2}x^2+\frac{4}{x-5}\) b) \(f(x)=\frac{3x+2}{x^2e^x}\)

Hints

- Differentiate the terms of a sum separately. - The denominator in part b is a product, so differentiate it with the product rule. - Factor common terms before canceling. - Recall the product rule for \(x^2e^x\).

Solution

1. For a), differentiate each term: \(f'(x)=x-\frac{4}{(x-5)^2}\). 2. For b), let \(u(x)=3x+2\) and \(v(x)=x^2e^x\). By the product rule, \(v'(x)=2xe^x+x^2e^x=xe^x(x+2)\). 3. Apply the quotient rule: \(f'(x)=\frac{3x^2e^x-(3x+2)xe^x(x+2)}{x^4e^{2x}}\). 4. Factor and cancel \(xe^x\): \(f'(x)=\frac{3x-(3x+2)(x+2)}{x^3e^x}\) \(=\frac{-3x^2-5x-4}{x^3e^x}\).

Answer

a) \(f'(x)=x-\frac{4}{(x-5)^2}\) b) \(f'(x)=\frac{-3x^2-5x-4}{x^3e^x}\)
52742612
Let \(f_k(x)=\frac{1-kx}{x^2}\), where \(k\in\mathbb{R}\) and \(x\ne 0\). Find \(f_k'(x)\) using both the quotient rule and the product rule. Show that the two results are equivalent.

Hints

- Treat \(k\) as a constant. - Rewrite \(x^{-2}\) carefully for the product-rule method. - Simplify the quotient-rule result by canceling a factor of \(x\). - Use a common denominator to compare the two forms.

Solution

1. Using the quotient rule, \(f_k'(x)=\frac{-kx^2-(1-kx)(2x)}{x^4}\) \(=\frac{kx^2-2x}{x^4}=\frac{kx-2}{x^3}\). 2. Rewrite the function as \(f_k(x)=(1-kx)x^{-2}\). By the product rule, \(f_k'(x)=-kx^{-2}+(1-kx)(-2x^{-3})\) \(=kx^{-2}-2x^{-3}\). 3. Combining the terms gives \(\frac{k}{x^2}-\frac{2}{x^3}=\frac{kx-2}{x^3}\), so the methods agree.

Answer

\(f_k'(x)=\frac{kx-2}{x^3}\), for \(x\ne 0\)
52742712
The illuminance \(I\), measured in lux, from an LED fixture is modeled by \(I(d)=\frac{800}{(d+2)^2}\), where \(d\ge0\) is the distance from the fixture in meters. a) Find \(I(0)\) and interpret the value in context. b) Expand the denominator, then use the quotient rule. Write the quotient-rule expression for \(I'(d)\) before simplifying it. Simplify \(I'(d)\) and determine its sign for \(d\ge0\). c) Find \(\lim_{d\to\infty}I(d)\) and interpret the result.

Hints

- Expand the squared denominator so differentiating it does not require a later rule. - In the quotient rule, identify the numerator and denominator functions before substituting their derivatives. - Determine the sign only after simplifying the derivative. - Interpret the limiting illuminance using the model's units.

Solution

1. \(I(0)=\frac{800}{4}=200\), so the modeled illuminance at \(d=0\) is \(200\,\text{lx}\). 2. Expand \((d+2)^2=d^2+4d+4\). With \(u(d)=800\) and \(v(d)=d^2+4d+4\), \(u'(d)=0\) and \(v'(d)=2d+4\). 3. The quotient-rule expression is \(I'(d)=\frac{0\cdot(d^2+4d+4)-800(2d+4)}{(d^2+4d+4)^2}\). 4. Simplifying gives \(I'(d)=-\frac{1600}{(d+2)^3}\). For \(d\ge0\), the denominator is positive, so \(I'(d)<0\). 5. As \(d\to\infty\), the denominator grows without bound, so \(I(d)\to0\). In the model, illuminance approaches \(0\,\text{lx}\) at very large distances.

Answer

a) \(200\,\text{lx}\); this is the modeled illuminance at \(d=0\) b) \(I'(d)=\frac{0\cdot(d^2+4d+4)-800(2d+4)}{(d^2+4d+4)^2}=-\frac{1600}{(d+2)^3}<0\) for \(d\ge0\) c) \(\lim_{d\to\infty}I(d)=0\); the modeled illuminance approaches \(0\,\text{lx}\)
52742812
After a medication is taken, its concentration in the blood is modeled by \(c(t)=\frac{10t}{t^2+4}\), where \(t\ge0\) is time in hours and \(c(t)\) is measured in \(\text{mg/L}\). a) Find the concentration at \(t=0\). b) Find \(c'(t)\) using the quotient rule. c) Analyze the monotonicity of \(c\) on \([0,2]\) and for \(t>2\). Interpret the results in context. d) Find the long-term limiting concentration.

Hints

- Substitute \(t=0\). - Apply the quotient rule carefully. - The denominator of the derivative is always positive, so analyze the numerator. - Compare the degrees of the numerator and denominator for the limit.

Solution

1. \(c(0)=0\,\text{mg/L}\). 2. Apply the quotient rule: \(c'(t)=\frac{10(t^2+4)-10t(2t)}{(t^2+4)^2}=\frac{40-10t^2}{(t^2+4)^2}\). 3. The denominator is always positive. The numerator is positive for \(0\le t<2\), zero at \(t=2\), and negative for \(t>2\). Therefore, the concentration increases on \([0,2]\) and decreases for \(t>2\). In the model, the medication level rises until \(2\) hours after administration and then falls. 4. Since the denominator has higher degree than the numerator, \(\lim_{t\to\infty}c(t)=0\). The modeled concentration approaches \(0\,\text{mg/L}\).

Answer

a) \(0\,\text{mg/L}\). b) \(c'(t)=\frac{40-10t^2}{(t^2+4)^2}\). c) Increasing on \([0,2]\); decreasing for \(t>2\). The concentration rises and then falls after reaching its peak at \(t=2\). d) \(0\,\text{mg/L}\).
52748512
Let \(f(x)=\frac{\sqrt{x^2+1}}{2x-3}\). Find and simplify \(f'(x)\).

Hints

- Use the quotient rule for the outer structure. - The radical in the numerator requires the chain rule. - Combine the numerator over a common radical denominator. - Distribute carefully when simplifying the numerator.

Solution

1. Let \(u(x)=\sqrt{x^2+1}\) and \(v(x)=2x-3\). Then \(u'(x)=\frac{x}{\sqrt{x^2+1}}\) and \(v'(x)=2\). 2. Apply the quotient rule: \(f'(x)=\frac{\frac{x}{\sqrt{x^2+1}}(2x-3)-2\sqrt{x^2+1}}{(2x-3)^2}\). 3. Combine the numerator over \(\sqrt{x^2+1}\): \(f'(x)=\frac{x(2x-3)-2(x^2+1)}{(2x-3)^2\sqrt{x^2+1}}=\frac{-3x-2}{(2x-3)^2\sqrt{x^2+1}}\).

Answer

\(f'(x)=\frac{-3x-2}{(2x-3)^2\sqrt{x^2+1}}\), where \(x\ne\frac{3}{2}\).
52749012
Let \(g(x)=\frac{e^{1-x}}{\sqrt{x^2+1}}\). Find \(g'(x)\).

Hints

- Use the quotient rule for the outer structure. - Apply the chain rule to both \(e^{1-x}\) and \(\sqrt{x^2+1}\). - Factor the common exponential expression from the numerator. - Combine the radical factors in the denominator carefully.

Solution

1. Let \(u(x)=e^{1-x}\) and \(v(x)=\sqrt{x^2+1}\). Then \(u'(x)=-e^{1-x}\) and \(v'(x)=\frac{x}{\sqrt{x^2+1}}\). 2. Apply the quotient rule: \(g'(x)=\frac{-e^{1-x}\sqrt{x^2+1}-e^{1-x}\frac{x}{\sqrt{x^2+1}}}{x^2+1}\). 3. Combine and simplify: \(g'(x)=-\frac{(x^2+x+1)e^{1-x}}{(x^2+1)\sqrt{x^2+1}}\).

Answer

\(g'(x)=-\frac{(x^2+x+1)e^{1-x}}{(x^2+1)\sqrt{x^2+1}}\)
52750112
Let \(f(x)=\frac{x+2}{\sqrt{x-2}}\) on its maximal domain. a) Find the domain. b) Show that \(f'(x)=\frac{0.5x-3}{\sqrt{(x-2)^3}}\). c) Find the point on the graph where the tangent line is horizontal.

Hints

- A square root in a denominator must be positive, not merely nonnegative. - Use the quotient rule and the chain rule. - Combine the numerator terms over a common denominator. - A horizontal tangent requires the first derivative to equal zero.

Solution

1. Because the square root is in the denominator, \(x-2\) must be strictly positive. Thus the domain is \((2,\infty)\). 2. Let \(u(x)=x+2\) and \(v(x)=\sqrt{x-2}\). Then \(u'(x)=1\) and \(v'(x)=\frac{1}{2\sqrt{x-2}}\). 3. The quotient rule gives \(f'(x)=\frac{\sqrt{x-2}-(x+2)\frac{1}{2\sqrt{x-2}}}{x-2}\). Combining terms yields \(f'(x)=\frac{x-6}{2\sqrt{(x-2)^3}}=\frac{0.5x-3}{\sqrt{(x-2)^3}}\). 4. A horizontal tangent requires \(f'(x)=0\). The denominator is positive on the domain, so \(0.5x-3=0\), giving \(x=6\). 5. Since \(f(6)=\frac{8}{2}=4\), the point is \((6,4)\).

Answer

a) \((2,\infty)\). b) \(f'(x)=\frac{0.5x-3}{\sqrt{(x-2)^3}}\). c) \((6,4)\).
52750212
Let \(g(x)=\frac{\sqrt{x^2+12}}{x}\), where \(x\neq0\). a) Show that \(g'(x)=-\frac{12}{x^2\sqrt{x^2+12}}\). b) Explain without further calculation why the graph has no horizontal tangent.

Hints

- Use the quotient rule and apply the chain rule to the square root. - Combine the two terms in the numerator over a common denominator. - A horizontal tangent requires the first derivative to be zero. - Check whether the numerator of the derivative can ever be zero.

Solution

1. Let \(u(x)=\sqrt{x^2+12}\) and \(v(x)=x\). Then \(u'(x)=\frac{x}{\sqrt{x^2+12}}\) and \(v'(x)=1\). 2. The quotient rule gives \(g'(x)=\frac{\frac{x}{\sqrt{x^2+12}}\cdot x-\sqrt{x^2+12}}{x^2}\). 3. Combining the numerator over a common denominator gives \(\frac{x^2-(x^2+12)}{\sqrt{x^2+12}}=\frac{-12}{\sqrt{x^2+12}}\). Therefore, \(g'(x)=-\frac{12}{x^2\sqrt{x^2+12}}\). 4. A horizontal tangent would require \(g'(x)=0\). The numerator is the nonzero constant \(-12\), while the denominator is positive on the domain, so the derivative is never zero.

Answer

a) \(g'(x)=-\frac{12}{x^2\sqrt{x^2+12}}\). b) The derivative has constant numerator \(-12\neq0\), so it has no zeros and the graph has no horizontal tangents.
52751512
Let \(f(x)=\frac{x}{\sqrt{x^2+4}}\). Determine whether the graph of \(f\) has symmetry about an axis or the origin. Then find \(f'(x)\) and determine whether its graph also has symmetry.

Hints

- Test \(f(-x)=f(x)\) for y-axis symmetry and \(f(-x)=-f(x)\) for origin symmetry. - Replace \(x\) with \(-x\) and compare expressions. - Use the quotient rule or rewrite the denominator with a negative exponent. - Squaring removes the sign of \(x\).

Solution

1. Evaluate \(f(-x)=\frac{-x}{\sqrt{x^2+4}}=-f(x)\). Therefore, \(f\) is odd, and its graph is symmetric about the origin. 2. Differentiate with the quotient rule: \(f'(x)=\frac{\sqrt{x^2+4}-x\left(\frac{x}{\sqrt{x^2+4}}\right)}{x^2+4}=\frac{4}{(x^2+4)\sqrt{x^2+4}}\). 3. Since \(f'(-x)=\frac{4}{(x^2+4)\sqrt{x^2+4}}=f'(x)\), the derivative is even, and its graph is symmetric about the y-axis.

Answer

The graph of \(f\) is symmetric about the origin. \(f'(x)=\frac{4}{(x^2+4)\sqrt{x^2+4}}\), and the graph of \(f'\) is symmetric about the y-axis.
52751712
Let \(f(x)=\frac{x+3}{\sqrt{x+1}}\) for \(x>-1\). Show algebraically that \(f'(x)=\frac{x-1}{2\sqrt{(x+1)^3}}\).

Hints

- Use the quotient rule. - Differentiate the square root with the chain rule. - Combine the terms in the numerator over a common denominator. - Use exponent rules to combine \((x+1)\sqrt{x+1}\).

Solution

1. Let \(u(x)=x+3\) and \(v(x)=\sqrt{x+1}\). Then \(u'(x)=1\) and \(v'(x)=\frac{1}{2\sqrt{x+1}}\). 2. Apply the quotient rule: \(f'(x)=\frac{\sqrt{x+1}-(x+3)\frac{1}{2\sqrt{x+1}}}{x+1}\). 3. Combine the numerator: \(f'(x)=\frac{2(x+1)-(x+3)}{2\sqrt{x+1}(x+1)}=\frac{x-1}{2\sqrt{x+1}(x+1)}\). 4. Since \((x+1)\sqrt{x+1}=\sqrt{(x+1)^3}\), \(f'(x)=\frac{x-1}{2\sqrt{(x+1)^3}}\).

Answer

\(f'(x)=\frac{x-1}{2\sqrt{(x+1)^3}}\)
52751812
Let \(g(x)=\frac{4x}{\sqrt{x^2+3}}\) for \(x\in\mathbb{R}\). Find and simplify \(g'(x)\).

Hints

- Apply the chain rule when differentiating the radical in the denominator. - Use the quotient rule for the outer structure. - Combine the numerator over a common radical denominator. - Look for terms that cancel after expansion.

Solution

1. Let \(u(x)=4x\) and \(v(x)=\sqrt{x^2+3}\). Then \(u'(x)=4\) and \(v'(x)=\frac{x}{\sqrt{x^2+3}}\). 2. Apply the quotient rule: \(g'(x)=\frac{4\sqrt{x^2+3}-4x\frac{x}{\sqrt{x^2+3}}}{x^2+3}\). 3. Combine the numerator: \(g'(x)=\frac{4(x^2+3)-4x^2}{(x^2+3)\sqrt{x^2+3}}=\frac{12}{(x^2+3)\sqrt{x^2+3}}\).

Answer

\(g'(x)=\frac{12}{(x^2+3)\sqrt{x^2+3}}\)
52755212
Let \(f(x)=\frac{\sqrt{4x+1}}{x}\). Find the largest real domain \(D_f\), and find \(f'(x)\).

Hints

- Check both the square-root condition and the denominator restriction. - Apply the quotient rule. - Differentiate the radical in the numerator with the chain rule. - Combine the resulting numerator over a common radical denominator.

Solution

1. The radicand condition gives \(x\ge-\frac{1}{4}\), and the denominator requires \(x\ne0\). Thus, \(D_f=\left[-\frac{1}{4},0\right)\cup(0,\infty)\). 2. Let \(u(x)=\sqrt{4x+1}\) and \(v(x)=x\). Then \(u'(x)=\frac{2}{\sqrt{4x+1}}\) and \(v'(x)=1\). 3. By the quotient rule, \(f'(x)=\frac{\frac{2x}{\sqrt{4x+1}}-\sqrt{4x+1}}{x^2}\). 4. Combine the numerator: \(f'(x)=\frac{2x-(4x+1)}{x^2\sqrt{4x+1}}=\frac{-2x-1}{x^2\sqrt{4x+1}}\).

Answer

\(D_f=\left[-\frac{1}{4},0\right)\cup(0,\infty)\); \(f'(x)=\frac{-2x-1}{x^2\sqrt{4x+1}}\) on the interior of \(D_f\)
52761212
Consider the family \(f_k(x)=\frac{x+k}{x}\), where \(k>0\) and \(x\neq 0\). Show that for every \(k\), there is a tangent line to the graph of \(f_k\) that passes through the origin. Find the point of tangency \(B\).

Hints

- Rewrite the function before differentiating. - Write the tangent line at a general x-coordinate \(x_0\). - Use the fact that the origin lies on the tangent line. - Substitute the resulting x-coordinate into the original function.

Solution

1. Rewrite the function as \(f_k(x)=1+\frac{k}{x}\), so \(f_k'(x)=-\frac{k}{x^2}\). 2. Let the point of tangency have x-coordinate \(x_0\). The tangent line is \(y=f_k'(x_0)(x-x_0)+f_k(x_0)\). 3. Since the line passes through \((0, 0)\), \(0=-\frac{k}{x_0^2}(0-x_0)+1+\frac{k}{x_0}\). 4. Simplify: \(0=1+\frac{2k}{x_0}\), so \(x_0=-2k\). Since \(k>0\), this is a valid domain value. 5. The y-coordinate is \(f_k(-2k)=\frac{-2k+k}{-2k}=\frac{1}{2}\). Therefore, \(B=\left(-2k, \frac{1}{2}\right)\).

Answer

\(B=\left(-2k, \frac{1}{2}\right)\)
52764412
Let \(f(x)=\frac{\ln(5x)}{x^2}\), where \(x>0\). a) Use the quotient rule and write the expression for \(f'(x)\) before simplifying it. b) Simplify your derivative.

Hints

- Use a logarithm property to determine the derivative of the numerator without a later Chain Rule. - Identify the numerator and denominator functions before applying the Quotient Rule. - Keep the quotient-rule numerator intact until part a is complete.

Solution

1. Since \(x>0\), \(\ln(5x)=\ln5+\ln x\), so the numerator derivative is \(\frac1x\). 2. With numerator \(u(x)=\ln(5x)\) and denominator \(v(x)=x^2\), the quotient rule gives \(f'(x)=\frac{(\frac1x)x^2-\ln(5x)(2x)}{x^4}\). 3. Simplifying gives \(f'(x)=\frac{1-2\ln(5x)}{x^3}\).

Answer

a) \(f'(x)=\frac{(\frac1x)x^2-\ln(5x)(2x)}{x^4}\) b) \(f'(x)=\frac{1-2\ln(5x)}{x^3}\)
52770012
For each function, find the maximal domain and the first derivative. a) \(h(x)=\ln(x^2+2x+2)\) b) \(k(x)=\frac{\ln(4x+1)}{x}\)

Hints

- Determine whether the quadratic in part a can ever be zero or negative. - Include both logarithm and denominator restrictions in part b. - Apply the chain rule to \(\ln(4x+1)\). - Use the quotient rule in part b.

Solution

1. Complete the square in part a: \(x^2+2x+2=(x+1)^2+1>0\) for every real \(x\). Therefore, \(D_h=\mathbb{R}\). Applying the chain rule, \(h'(x)=\frac{2x+2}{x^2+2x+2}\). 2. For part b, require \(4x+1>0\), so \(x>-\frac{1}{4}\), and also require \(x\ne0\). Thus, \(D_k=\left(-\frac{1}{4}, 0\right)\cup(0, \infty)\). Using the quotient rule, \(k'(x)=\frac{\frac{4x}{4x+1}-\ln(4x+1)}{x^2}\). Combining the numerator gives \(k'(x)=\frac{4x-(4x+1)\ln(4x+1)}{x^2(4x+1)}\).

Answer

a) \(D_h=\mathbb{R}\), \(h'(x)=\frac{2x+2}{x^2+2x+2}\) b) \(D_k=\left(-\frac{1}{4}, 0\right)\cup(0, \infty)\), \(k'(x)=\frac{4x-(4x+1)\ln(4x+1)}{x^2(4x+1)}\)
52791212
Let \(g(x)=\frac{e^x}{e^x+2}\). a) Find \(g'(x)\). b) Find the limits as \(x\to\infty\) and as \(x\to-\infty\), and state the equations of the horizontal asymptotes.

Hints

- Use the quotient rule. - Determine what happens to \(e^x\) as \(x\to-\infty\). - For \(x\to\infty\), divide the numerator and denominator by \(e^x\). - A finite end-behavior limit gives a horizontal asymptote.

Solution

1. Apply the quotient rule: \(g'(x)=\frac{e^x(e^x+2)-e^x(e^x)}{(e^x+2)^2}=\frac{2e^x}{(e^x+2)^2}\). 2. As \(x\to-\infty\), \(e^x\to0\), so \(g(x)\to0\). Thus, \(y=0\) is a horizontal asymptote. 3. As \(x\to\infty\), divide numerator and denominator by \(e^x\): \(g(x)=\frac{1}{1+2e^{-x}}\to1\). Thus, \(y=1\) is a horizontal asymptote.

Answer

a) \(g'(x)=\frac{2e^x}{(e^x+2)^2}\) b) \(\lim_{x\to-\infty}g(x)=0\) and \(\lim_{x\to\infty}g(x)=1\); horizontal asymptotes: \(y=0\) and \(y=1\)
52899612
A common error is to differentiate the numerator and denominator of a quotient separately. Let \(k(x)=\frac{x^6}{x^2}\), where \(x\neq0\). a) Use the quotient rule to find \(k'(x)\). b) Find the quotient of the derivative of the numerator and the derivative of the denominator. c) Compare the results. Does separate differentiation give the correct derivative for every \(x>0\)?

Hints

- Use \(\left(\frac{u}{v}\right)'=\frac{u'v-uv'}{v^2}\) for the first derivative of a quotient. - Differentiate the numerator and denominator separately only for the comparison in part b). - Determine whether the two resulting expressions are equal for every allowed input.

Solution

1. By the quotient rule, \(k'(x)=\frac{(6x^5)(x^2)-(x^6)(2x)}{(x^2)^2}\). 2. Simplify: \(k'(x)=\frac{6x^7-2x^7}{x^4}=4x^3\). 3. Differentiating numerator and denominator separately and dividing gives \(\frac{6x^5}{2x}=3x^4\). 4. The expressions \(4x^3\) and \(3x^4\) are equal only when \(x=\frac{4}{3}\) in the domain \(x>0\). They are not identical, so separate differentiation is not a valid quotient rule.

Answer

a) \(k'(x)=4x^3\) b) \(3x^4\) c) No. The expressions agree only at \(x=\frac{4}{3}\), not for every \(x>0\).
52947112
Use the quotient rule to find the derivative of each function. a) \(f(x)=\frac{2x^2-5}{3x+4}\) b) \(g(x)=\frac{\cos(x)}{x^2}\)

Hints

- Identify the numerator and denominator in each part. - Differentiate those components separately. - Track the subtraction in the quotient-rule numerator. - Factor a common \(x\) in part b to simplify.

Solution

1. For a), \(f'(x)=\frac{4x(3x+4)-3(2x^2-5)}{(3x+4)^2}\) \(=\frac{6x^2+16x+15}{(3x+4)^2}\). 2. For b), \(g'(x)=\frac{-\sin(x)x^2-\cos(x)(2x)}{x^4}\) \(=\frac{-x\sin(x)-2\cos(x)}{x^3}\).

Answer

a) \(f'(x)=\frac{6x^2+16x+15}{(3x+4)^2}\), for \(x\ne-\frac{4}{3}\) b) \(g'(x)=\frac{-x\sin(x)-2\cos(x)}{x^3}\), for \(x\ne 0\)
52947212
Consider functions of the form \(h(x)=\frac{c}{v(x)}\), where \(c\) is a real constant. a) Use the quotient rule to show that when \(c=1\), \(h'(x)=-\frac{v'(x)}{(v(x))^2}\). b) Use this reciprocal rule or the quotient rule to find the derivative of \(f(x)=\frac{5}{x^2+\sin(x)}\).

Hints

- In the quotient rule, the derivative of a constant numerator is zero. - Constant factors remain when differentiating. - Differentiate the denominator in part b first.

Solution

1. For a), let the numerator be \(u(x)=1\). Then \(u'(x)=0\). By the quotient rule, \(h'(x)=\frac{0\cdot v(x)-1\cdot v'(x)}{(v(x))^2}\) \(=-\frac{v'(x)}{(v(x))^2}\). 2. For b), let \(v(x)=x^2+\sin(x)\). Then \(v'(x)=2x+\cos(x)\). Thus, \(f'(x)=-5\frac{2x+\cos(x)}{(x^2+\sin(x))^2}\) \(=-\frac{10x+5\cos(x)}{(x^2+\sin(x))^2}\).

Answer

a) \(h'(x)=-\frac{v'(x)}{(v(x))^2}\), wherever \(v(x)\ne 0\) b) \(f'(x)=-\frac{10x+5\cos(x)}{(x^2+\sin(x))^2}\), wherever \(x^2+\sin(x)\ne 0\)
52947912
Suppose \(f(x)=\frac{u(x)}{v(x)w(x)}\), where \(u\), \(v\), and \(w\) are differentiable and \(v(x)\ne 0\), \(w(x)\ne 0\). Derive a formula for \(f'(x)\). Use the quotient rule for the overall fraction and the product rule for the denominator. Expand all terms in the numerator.

Hints

- Treat the product in the denominator as one function first. - Apply the quotient rule to the full fraction. - Use the product rule when differentiating the denominator. - Distribute the negative sign across both terms.

Solution

1. Treat \(v(x)w(x)\) as the denominator. By the quotient rule, \(f'(x)=\frac{u'(x)v(x)w(x)-u(x)[v(x)w(x)]'}{[v(x)w(x)]^2}\). 2. By the product rule, \([v(x)w(x)]'=v'(x)w(x)+v(x)w'(x)\). 3. Substitute and distribute the negative sign: \(f'(x)=\frac{u'(x)v(x)w(x)-u(x)v'(x)w(x)-u(x)v(x)w'(x)}{v(x)^2w(x)^2}\).

Answer

\(f'(x)=\frac{u'(x)v(x)w(x)-u(x)v'(x)w(x)-u(x)v(x)w'(x)}{v(x)^2w(x)^2}\)
52948012
Find and simplify the derivative of \(h(x)=\frac{x\sin(x)}{e^x}\).

Hints

- The function contains both a product and a quotient. - Differentiate the numerator and denominator separately first. - Factor the common exponential term before simplifying.

Solution

1. Let \(u(x)=x\sin(x)\) and \(v(x)=e^x\). 2. By the product rule, \(u'(x)=\sin(x)+x\cos(x)\), and \(v'(x)=e^x\). 3. Apply the quotient rule: \(h'(x)=\frac{[\sin(x)+x\cos(x)]e^x-x\sin(x)e^x}{e^{2x}}\). 4. Factor and cancel \(e^x\): \(h'(x)=\frac{\sin(x)+x\cos(x)-x\sin(x)}{e^x}\) \(=\frac{(1-x)\sin(x)+x\cos(x)}{e^x}\).

Answer

\(h'(x)=\frac{(1-x)\sin(x)+x\cos(x)}{e^x}\)
52948312
Let \(f(x)=\frac{x^2-4x+5}{x-2}\), where \(x\ne 2\). Find \(f'(x)\) in two ways. 1) First perform polynomial division, and then differentiate the resulting sum. 2) Apply the quotient rule directly to the original expression. Show algebraically that the two results are equivalent.

Hints

- Use polynomial division to rewrite the rational expression. - Differentiate the reciprocal term using a negative exponent. - Keep the subtraction in the quotient-rule numerator. - Use a common denominator to compare the two forms.

Solution

1. Polynomial division gives \(f(x)=x-2+\frac{1}{x-2}\). Therefore, \(f'(x)=1-\frac{1}{(x-2)^2}\). 2. By the quotient rule, \(f'(x)=\frac{(2x-4)(x-2)-(x^2-4x+5)}{(x-2)^2}\) \(=\frac{x^2-4x+3}{(x-2)^2}\). 3. Put the first result over a common denominator: \(1-\frac{1}{(x-2)^2}=\frac{(x-2)^2-1}{(x-2)^2}\) \(=\frac{x^2-4x+3}{(x-2)^2}\). Thus, the methods agree.

Answer

\(f'(x)=1-\frac{1}{(x-2)^2}=\frac{x^2-4x+3}{(x-2)^2}\)
52948512
Derive the power rule for negative integer exponents by differentiating \(f(x)=x^{-n}=\frac{1}{x^n}\), where \(n\) is a positive integer and \(x\ne 0\), using the quotient rule. Then find the derivative of \(g(x)=\frac{3}{x^5}\).

Hints

- Apply the quotient rule to \(\frac{1}{x^n}\). - The derivative of the constant numerator is zero. - Use exponent rules to simplify the quotient. - Treat the factor \(3\) as a constant.

Solution

1. For \(f(x)=\frac{1}{x^n}\), let \(u(x)=1\) and \(v(x)=x^n\). Then \(u'(x)=0\) and \(v'(x)=nx^{n-1}\). 2. By the quotient rule, \(f'(x)=\frac{0\cdot x^n-nx^{n-1}}{x^{2n}}\) \(=-n x^{n-1-2n}=-n x^{-n-1}\). 3. Apply the rule to \(g(x)=3x^{-5}\): \(g'(x)=3\cdot(-5)x^{-6}=-\frac{15}{x^6}\).

Answer

\(\frac{d}{dx}x^{-n}=-n x^{-n-1}\). For \(g(x)=\frac{3}{x^5}\), \(g'(x)=-\frac{15}{x^6}\).
52948612
Let \(h(x)=\frac{x^2-5}{x^4}\), where \(x\ne 0\). Find \(h'(x)\) in two ways. 1) Apply the quotient rule directly. 2) Rewrite the function as a sum of negative powers and use the power rule. Show that the two methods give the same result.

Hints

- Divide each numerator term by \(x^4\) to obtain negative powers. - Track the subtraction in the quotient-rule numerator. - Rewrite both derivative forms with a common denominator to compare them. - Simplify the quotient-rule result by factoring powers of \(x\).

Solution

1. By the quotient rule, \(h'(x)=\frac{2x(x^4)-(x^2-5)(4x^3)}{x^8}\) \(=\frac{-2x^5+20x^3}{x^8}=\frac{-2x^2+20}{x^5}\). 2. Rewrite the function as \(h(x)=x^{-2}-5x^{-4}\). Then \(h'(x)=-2x^{-3}+20x^{-5}\). 3. Put the second result over the common denominator \(x^5\): \(-2x^{-3}+20x^{-5}=\frac{-2x^2+20}{x^5}\). Thus, the methods agree.

Answer

\(h'(x)=\frac{-2x^2+20}{x^5}=-2x^{-3}+20x^{-5}\)
52948812
Let \(f(x)=\frac{\sqrt{x}}{\cos(x)-x}\). Use the quotient rule to find \(f'(x)\), and state the domain of the derivative.

Hints

- Rewrite the square root as a fractional power if helpful. - Track the signs when differentiating the denominator. - Keep parentheses around each quotient-rule component. - Clear the small fraction in the numerator using a common factor.

Solution

1. Let \(u(x)=\sqrt{x}\) and \(v(x)=\cos(x)-x\). Then \(u'(x)=\frac{1}{2\sqrt{x}}\) and \(v'(x)=-\sin(x)-1\). 2. By the quotient rule, \(f'(x)=\frac{\frac{1}{2\sqrt{x}}(\cos(x)-x)-\sqrt{x}(-\sin(x)-1)}{(\cos(x)-x)^2}\). 3. Multiply the numerator by a common factor of \(2\sqrt{x}\) and simplify: \(f'(x)=\frac{\cos(x)+x+2x\sin(x)}{2\sqrt{x}(\cos(x)-x)^2}\). The derivative is defined when \(x>0\) and \(\cos(x)\ne x\).

Answer

\(f'(x)=\frac{\cos(x)+x+2x\sin(x)}{2\sqrt{x}(\cos(x)-x)^2}\), with domain \(\{x\in\mathbb{R}:x>0\text{ and }\cos(x)\ne x\}\)
52949712
Let \(f(x)=\frac{2x^3-5}{x^2+4}\). 1. Use the quotient rule to find \(f'(x)\). Simplify the numerator. 2. State the degree of the numerator of \(f(x)\) and the degree of the numerator of \(f'(x)\). 3. Explain why differentiation did not lower the numerator degree in this example.

Hints

- Write the quotient rule before substituting. - Compare the degrees of the two products in the derivative numerator. - Check whether the leading terms cancel after subtraction. - Base your explanation on the simplified numerator.

Solution

1. Let \(u(x)=2x^3-5\) and \(v(x)=x^2+4\). Then \(u'(x)=6x^2\) and \(v'(x)=2x\). By the quotient rule, \(f'(x)=\frac{6x^2(x^2+4)-2x(2x^3-5)}{(x^2+4)^2}\) \(=\frac{6x^4+24x^2-4x^4+10x}{(x^2+4)^2}\) \(=\frac{2x^4+24x^2+10x}{(x^2+4)^2}\). 2. The numerator of \(f\) has degree \(3\). The simplified numerator of \(f'\) has degree \(4\). 3. In the quotient-rule numerator, both \(u'v\) and \(uv'\) have degree \(4\). Their leading terms are \(6x^4\) and \(4x^4\), so subtraction leaves the nonzero leading term \(2x^4\). Therefore, the numerator degree is \(4\), not less than \(3\).

Answer

1. \(f'(x)=\frac{2x^4+24x^2+10x}{(x^2+4)^2}\) 2. Original numerator degree: \(3\); derivative numerator degree: \(4\). 3. The two degree- \(4\) leading terms in the quotient-rule numerator do not cancel, so the simplified numerator still has degree \(4\).
52949912
Let \(f(x)=\frac{\sin x}{1+\cos x}\). Use the quotient rule to find \(f'(x)\), and simplify the result to show that \(f'(x)=\frac{1}{1+\cos x}\).

Hints

- Use the quotient rule. - Differentiate sine and cosine carefully. - Look for the identity \(\sin^2x+\cos^2x=1\) in the numerator. - Cancel a common factor only after factoring the numerator.

Solution

1. Let \(u(x)=\sin x\) and \(v(x)=1+\cos x\). Then \(u'(x)=\cos x\) and \(v'(x)=-\sin x\). 2. Apply the quotient rule: \(f'(x)=\frac{\cos x(1+\cos x)-\sin x(-\sin x)}{(1+\cos x)^2}\). 3. Simplify the numerator using \(\sin^2x+\cos^2x=1\): \(\cos x+\cos^2x+\sin^2x=1+\cos x\). Therefore, \(f'(x)=\frac{1+\cos x}{(1+\cos x)^2}=\frac{1}{1+\cos x}\). The original function and its derivative are defined when \(x\ne (2k+1)\pi\), where \(k\in\mathbb{Z}\).

Answer

\(f'(x)=\frac{1}{1+\cos x}\), for \(x\ne (2k+1)\pi\), \(k\in\mathbb{Z}\)
52950012
Let \(f(x)=\frac{\tan x}{1+\tan x}\). Use \(\frac{d}{dx}(\tan x)=1+\tan^2x\) and the quotient rule to find \(f'(x)\). Simplify the numerator as much as possible.

Hints

- Apply the quotient rule before simplifying. - Use the given derivative for both occurrences of \(\tan x\). - Factor the common expression in the numerator instead of expanding it. - Check both restrictions in the original function.

Solution

1. Let \(u(x)=\tan x\) and \(v(x)=1+\tan x\). Then \(u'(x)=v'(x)=1+\tan^2x\). 2. Apply the quotient rule: \(f'(x)=\frac{(1+\tan^2x)(1+\tan x)-\tan x(1+\tan^2x)}{(1+\tan x)^2}\). 3. Factor the common expression in the numerator: \(f'(x)=\frac{(1+\tan^2x)[(1+\tan x)-\tan x]}{(1+\tan x)^2}\). Therefore, \(f'(x)=\frac{1+\tan^2x}{(1+\tan x)^2}\). The domain excludes values where \(\tan x\) is undefined and values where \(\tan x=-1\).

Answer

\(f'(x)=\frac{1+\tan^2x}{(1+\tan x)^2}\), for \(x\ne \frac{\pi}{2}+k\pi\) and \(x\ne -\frac{\pi}{4}+k\pi\), \(k\in\mathbb{Z}\)
52951412
Find the derivative of \(f(x)=\frac{5}{x^2+3}\) in two ways. 1) Apply the quotient rule. 2) Rewrite the function using a negative exponent, and apply the chain rule. Verify that the two methods give the same result.

Hints

- In the quotient rule, the derivative of the constant numerator is zero. - Rewrite \(\frac{1}{z}\) as \(z^{-1}\) for the chain-rule method. - Track the negative sign and the new exponent carefully.

Solution

1. Using the quotient rule with numerator \(5\) and denominator \(x^2+3\), \(f'(x)=\frac{0(x^2+3)-5(2x)}{(x^2+3)^2}\) \(=-\frac{10x}{(x^2+3)^2}\). 2. Rewrite the function as \(f(x)=5(x^2+3)^{-1}\). Using the chain rule, \(f'(x)=5[-(x^2+3)^{-2}](2x)\) \(=-\frac{10x}{(x^2+3)^2}\). The two methods agree.

Answer

\(f'(x)=-\frac{10x}{(x^2+3)^2}\)
52952412
Let \(f(x)=\sqrt{\frac{3x+2}{x^2+1}}\). Find \(f'(x)\) using the chain rule and quotient rule.

Hints

- Treat the square root as the outer function. - Use the quotient rule on the expression under the radical. - Multiply the outer derivative by the inner derivative. - Track signs carefully when expanding the quotient-rule numerator.

Solution

1. Let \(r(x)=\frac{3x+2}{x^2+1}\). The outer function is \(\sqrt{r}\), whose derivative is \(\frac{1}{2\sqrt{r}}\). 2. By the quotient rule, \(r'(x)=\frac{3(x^2+1)-(3x+2)(2x)}{(x^2+1)^2}\) \(=\frac{-3x^2-4x+3}{(x^2+1)^2}\). 3. Apply the chain rule: \(f'(x)=\frac{1}{2\sqrt{\frac{3x+2}{x^2+1}}}\left(\frac{-3x^2-4x+3}{(x^2+1)^2}\right)\) \(=\frac{-3x^2-4x+3}{2(x^2+1)^2\sqrt{\frac{3x+2}{x^2+1}}}\). The derivative is defined for \(x>-\frac{2}{3}\).

Answer

\(f'(x)=\frac{-3x^2-4x+3}{2(x^2+1)^2\sqrt{\frac{3x+2}{x^2+1}}}\), for \(x>-\frac{2}{3}\)
52952712
Let \(f(x)=\frac{4x+2}{x-1}\). At which x-values is the tangent line to the graph of \(f\) parallel to the line \(6x+y=4\)?

Hints

- Rewrite the line in slope-intercept form. - Parallel lines have equal slopes. - The derivative gives the slope of the tangent line. - Which derivative rule applies to a quotient?

Solution

1. Rewrite the given line as \(y=-6x+4\), so its slope is \(-6\). 2. Differentiate using the quotient rule: \(f'(x)=\frac{4(x-1)-(4x+2)}{(x-1)^2}=\frac{-6}{(x-1)^2}\). 3. Parallel tangent lines must have slope \(-6\), so solve \(\frac{-6}{(x-1)^2}=-6\). 4. This gives \((x-1)^2=1\), so \(x-1=\pm1\). Therefore, \(x=0\) or \(x=2\). Both values are in the domain of \(f\).

Answer

\(x=0\) and \(x=2\)
52953312
For \(k\in\mathbb{R}\), let \(f_k(x)=\frac{kx}{\sqrt{x^2+1}}\). Find and simplify \(f_k'(x)\).

Hints

- Use the quotient rule for the outer structure. - Apply the chain rule to the radical denominator. - Combine the numerator over a common radical denominator. - Use exponent rules to simplify the final denominator.

Solution

1. Let \(u(x)=kx\) and \(v(x)=\sqrt{x^2+1}\). Then \(u'(x)=k\) and \(v'(x)=\frac{x}{\sqrt{x^2+1}}\). 2. By the quotient rule, \(f_k'(x)=\frac{k\sqrt{x^2+1}-kx\frac{x}{\sqrt{x^2+1}}}{x^2+1}\). 3. Combine the numerator: \(f_k'(x)=\frac{k(x^2+1)-kx^2}{(x^2+1)\sqrt{x^2+1}}=\frac{k}{(x^2+1)^{\frac{3}{2}}}\).

Answer

\(f_k'(x)=\frac{k}{(x^2+1)^{\frac{3}{2}}}\)
52953612
Consider the family \(g_k(x)=\frac{x}{x^2+k}\), where \(k>0\) and \(x\in\mathbb{R}\). 1. Use the quotient rule to find \(g_k'(x)\). 2. Find the local maximum in terms of \(k\). 3. Find the equation of the locus containing all local maxima. Method requirement: For every conclusion that a local extremum occurs, show the sign of the relevant first derivative on the two sides of the critical number and explicitly use the first derivative test. A critical-number calculation alone is not sufficient.

Hints

- Identify the numerator and denominator before applying the quotient rule. - The denominator of the derivative is always positive. - Use a sign change to determine which critical point is the local maximum. - Eliminate \(k\) from the maximum coordinates.

Solution

1. The quotient rule gives \(g_k'(x)=\frac{(x^2+k)-x(2x)}{(x^2+k)^2}=\frac{k-x^2}{(x^2+k)^2}\). 2. The denominator is positive, so critical points satisfy \(k-x^2=0\), giving \(x=\pm\sqrt{k}\). The derivative changes from positive to negative at \(x=\sqrt{k}\), so the local maximum is \(\left(\sqrt{k}, \frac{1}{2\sqrt{k}}\right)\). 3. At the maximum, \(x=\sqrt{k}>0\), so \(k=x^2\). Substituting into the y-coordinate gives \(y=\frac{1}{2x}\). Thus the locus is \(y=\frac{1}{2x}\) for \(x>0\).

Answer

1. \(g_k'(x)=\frac{k-x^2}{(x^2+k)^2}\) 2. \(\left(\sqrt{k}, \frac{1}{2\sqrt{k}}\right)\) 3. \(y=\frac{1}{2x}\) for \(x>0\)
52990812
Let \(f(x)=\frac4x\) for \(x>0\). A tangent line touches the graph at \(P(x_0,f(x_0))\), crosses the x-axis at \(S_x\), and crosses the y-axis at \(S_y\). a) Use the quotient rule. Write the quotient-rule expression for \(f'(x)\) before simplifying it. b) Use that derivative to show algebraically that \(P\) is always the midpoint of \(\overline{S_xS_y}\).

Hints

- Complete the Quotient Rule setup before using the tangent geometry. - Write the tangent at a general input \(x_0\) using the derivative you obtained. - Find the two axis intercepts separately, then apply the midpoint formula.

Solution

1. With numerator \(4\) and denominator \(x\), the quotient rule gives \(f'(x)=\frac{0\cdot x-4\cdot1}{x^2}=-\frac4{x^2}\). 2. At \(P(x_0,\frac4{x_0})\), the tangent is \(y=-\frac4{x_0^2}(x-x_0)+\frac4{x_0}=-\frac4{x_0^2}x+\frac8{x_0}\). 3. Setting \(x=0\) gives \(S_y=(0,\frac8{x_0})\). Setting \(y=0\) gives \(S_x=(2x_0,0)\). 4. Their midpoint is \(\left(\frac{2x_0}{2},\frac{8/x_0}{2}\right)=\left(x_0,\frac4{x_0}\right)=P\).

Answer

a) \(f'(x)=\frac{0\cdot x-4\cdot1}{x^2}=-\frac4{x^2}\) b) \(S_x=(2x_0,0)\), \(S_y=(0,\frac8{x_0})\), and their midpoint is \((x_0,\frac4{x_0})=P\).
52999012
Find the first derivative of each function, where \(x>0\). a) \(g(x)=\frac{\ln x}{x+1}\) b) \(h(x)=\frac{\ln(x^2)}{x}\)

Hints

- Use the quotient rule directly in part a. - In part b, simplify the logarithm with a power property before applying the quotient rule. - Keep the domain restriction in mind when using logarithm identities.

Solution

1. For part a, apply the quotient rule: \(g'(x)=\frac{\frac{1}{x}(x+1)-\ln x}{(x+1)^2}\). 2. Combining the numerator over \(x\) gives \(g'(x)=\frac{x+1-x\ln x}{x(x+1)^2}\). 3. For part b, since \(x>0\), \(\ln(x^2)=2\ln x\). Thus \(h(x)=\frac{2\ln x}{x}\). 4. Applying the quotient rule gives \(h'(x)=\frac{2-2\ln x}{x^2}\).

Answer

a) \(g'(x)=\frac{x+1-x\ln x}{x(x+1)^2}\) b) \(h'(x)=\frac{2-2\ln x}{x^2}\)
53007712
Consider the family \(f_k(x)=\frac{x^2}{x-k}\), where \(x\neq k\) and \(k\in\mathbb{R}\setminus\{0\}\). a) Find the coordinates of the local extrema in terms of \(k\). b) Show that all of these extrema lie on the line \(y=2x\). Method requirement: For every conclusion that a local extremum occurs, show the sign of the relevant first derivative on the two sides of the critical number and explicitly use the first derivative test. A critical-number calculation alone is not sufficient.

Hints

- Apply the quotient rule and factor the numerator. - Check that each critical point belongs to the domain. - Use a sign chart to classify the extrema. - Substitute each point into the line equation.

Solution

1. By the quotient rule, \(f_k'(x)=\frac{2x(x-k)-x^2}{(x-k)^2}=\frac{x(x-2k)}{(x-k)^2}\). 2. The critical points are \(x=0\) and \(x=2k\), both of which are in the domain because \(k\neq0\). Their coordinates are \((0, 0)\) and \((2k, 4k)\). 3. The derivative changes sign at each critical point, so both are local extrema. Their classifications depend on the sign of \(k\): for \(k>0\), \((0, 0)\) is a local maximum and \((2k, 4k)\) is a local minimum; for \(k<0\), the classifications are reversed. 4. Both points satisfy \(y=2x\): \(0=2(0)\) and \(4k=2(2k)\).

Answer

a) \((0, 0)\) and \((2k, 4k)\). For \(k>0\), they are a local maximum and local minimum, respectively; for \(k<0\), the classifications are reversed. b) \(y=2x\)
53009512
Consider the family \(f_t(x)=\frac{tx^2}{x-t}\), where \(t\in\mathbb{R}\setminus\{0\}\). Show algebraically that every local extremum of the family lies on the parabola \(y=x^2\). Method requirement: For every conclusion that a local extremum occurs, show the sign of the relevant first derivative on the two sides of the critical number and explicitly use the first derivative test. A critical-number calculation alone is not sufficient.

Hints

- Apply the quotient rule and factor the derivative. - Check that the critical points are in the domain. - Evaluate the function at each critical point. - Substitute each point into \(y=x^2\).

Solution

1. By the quotient rule, \(f_t'(x)=\frac{2tx(x-t)-tx^2}{(x-t)^2}=\frac{tx(x-2t)}{(x-t)^2}\). 2. The critical points are \(x=0\) and \(x=2t\). Both are in the domain because \(t\neq0\). 3. Their coordinates are \((0, 0)\) and \((2t, 4t^2)\). A sign chart for the derivative confirms that both are local extrema. 4. The first point satisfies \(0=0^2\), and the second satisfies \(4t^2=(2t)^2\). Therefore, every local extremum lies on \(y=x^2\).

Answer

The local extrema are \((0, 0)\) and \((2t, 4t^2)\), and both satisfy \(y=x^2\).
53009812
Let \(f(x)=\frac{ax^2+bx}{x-2}\). Find \(a\) and \(b\) so that the graph has a horizontal tangent at \(x=0\) and passes through \(P(4, 8)\).

Hints

- Use the given point to obtain one equation in the parameters. - A horizontal tangent gives a condition on the first derivative. - Apply the quotient rule before substituting the tangent input.

Solution

1. The point condition gives \(f(4)=8\): \(\frac{16a+4b}{2}=8\), so \(4a+b=4\). 2. By the quotient rule, \(f'(x)=\frac{(2ax+b)(x-2)-(ax^2+bx)}{(x-2)^2}=\frac{ax^2-4ax-2b}{(x-2)^2}\). 3. A horizontal tangent at \(x=0\) requires \(f'(0)=0\), so \(b=0\). 4. Substituting \(b=0\) into \(4a+b=4\) gives \(a=1\).

Answer

\(a=1\) and \(b=0\)
53017112
Let \(f(x)=\frac{e^x}{x}\) for \(x\ne0\). a) Use the quotient rule and write the expression for \(f'(x)\) before simplifying it. b) Find the slope \(k\) of a line through the origin, \(g(x)=kx\), that is tangent to the graph of \(f\). Also find the point of tangency.

Hints

- Write the Quotient Rule setup before simplifying the derivative. - At a tangency point, the function values agree and the slopes agree. - Eliminate \(k\) to obtain an equation involving only the tangency input.

Solution

1. The quotient rule gives \(f'(x)=\frac{e^x x-e^x}{x^2}=\frac{e^x(x-1)}{x^2}\). 2. Let the tangency input be \(x_0\). Tangency requires \(f(x_0)=kx_0\) and \(f'(x_0)=k\). 3. Substitute \(k=f'(x_0)\): \(\frac{e^{x_0}}{x_0}=\frac{e^{x_0}(x_0-1)}{x_0^2}x_0\). 4. Since \(x_0\ne0\) and \(e^{x_0}>0\), this reduces to \(1=x_0-1\), so \(x_0=2\). 5. Therefore, \(k=f'(2)=\frac{e^2}{4}\), and the point of tangency is \((2,\frac{e^2}{2})\).

Answer

a) \(f'(x)=\frac{e^x x-e^x}{x^2}=\frac{e^x(x-1)}{x^2}\) b) \(k=\frac{e^2}{4}\); point of tangency \(\left(2,\frac{e^2}{2}\right)\)
53451612
Let \(g(x)=\frac{x^2-3x}{x+2}\). Use the quotient rule to find the slope of the graph at \(x=1\).

Hints

- Differentiate the numerator and denominator separately before applying the quotient rule. - Keep the subtraction in the quotient-rule numerator grouped. - Substitute the requested input after simplifying the derivative.

Solution

1. Let \(u(x)=x^2-3x\) and \(v(x)=x+2\). Then \(u'(x)=2x-3\) and \(v'(x)=1\). 2. Apply the quotient rule: \(g'(x)=\frac{(2x-3)(x+2)-(x^2-3x)}{(x+2)^2}=\frac{x^2+4x-6}{(x+2)^2}\). 3. Evaluate at \(x=1\): \(g'(1)=-\frac{1}{9}\).

Answer

\(g'(1)=-\frac{1}{9}\)
53454912
Let \(k(x)=\frac{2x^2}{x^2+2}\). Find the equation of the tangent line at \(P(2,k(2))\). Then find the angle the tangent line makes with the positive x-axis, rounded to two decimal places.

Hints

- Find the point's y-coordinate before writing the tangent line. - Use the quotient rule to determine the tangent slope. - Convert the final positive slope to an inclination angle with inverse tangent.

Solution

1. Evaluate the function: \(k(2)=\frac{4}{3}\), so \(P=\left(2,\frac{4}{3}\right)\). 2. By the quotient rule, \(k'(x)=\frac{4x(x^2+2)-4x^3}{(x^2+2)^2}=\frac{8x}{(x^2+2)^2}\). 3. The tangent slope is \(m=k'(2)=\frac{4}{9}\). 4. Point-slope form gives \(y-\frac{4}{3}=\frac{4}{9}(x-2)\), so \(y=\frac{4}{9}x+\frac{4}{9}\). 5. The inclination angle satisfies \(\tan(\alpha)=\frac{4}{9}\), so \(\alpha\approx23.96^\circ\).

Answer

The tangent line is \(y=\frac{4}{9}x+\frac{4}{9}\), and its angle with the positive x-axis is approximately \(23.96^\circ\).
53459212
Consider the family \(f_a(x)=\frac{a\ln x}{x}\), where \(x>0\) and \(a\ne0\). The figure shows the graphs \(p\) and \(q\) for \(a=2\) and \(a=4\), respectively. Use the figure to conjecture whether their extrema share an x-coordinate. a) Find \(a\) so that the graph passes through \(P(e^2,2)\). b) Prove that every family member has its only critical point at \(x=e\). Classify that point as a local maximum or local minimum according to the sign of \(a\), and give the equation of the line containing all such extrema. c) Find the tangent slope at the zero \(x=1\) in terms of \(a\). Method requirement: For every conclusion that a local extremum occurs, show the sign of the relevant first derivative on the two sides of the critical number and explicitly use the first derivative test. A critical-number calculation alone is not sufficient.
Figure for problem 534592

Hints

- Use the two displayed graphs to form a conjecture about the x-coordinate of the extremum, then prove it from the derivative. - Factor the derivative so its sign can be determined without a second derivative. - Compare the sign of \(1-\ln x\) on the two sides of \(e\), then account for the sign of \(a\).

Solution

1. The two displayed positive-\(a\) graphs suggest that their extrema occur at the same x-coordinate. 2. a) Substituting \(P(e^2,2)\) gives \(\frac{2a}{e^2}=2\), so \(a=e^2\). 3. b) The quotient rule gives \(f_a'(x)=a\frac{1-\ln x}{x^2}\). Since \(a\ne0\) and \(x^2>0\), the only critical point occurs when \(\ln x=1\), so \(x=e\). 4. The factor \(1-\ln x\) is positive for \(0<x<e\) and negative for \(x>e\). Therefore, if \(a>0\), \(f_a'\) changes from positive to negative and \(x=e\) is a local maximum. If \(a<0\), the signs reverse and \(x=e\) is a local minimum. 5. Every extremum has x-coordinate \(e\), so all extrema lie on the vertical line \(x=e\). 6. c) At the zero \(x=1\), \(f_a'(1)=a\).

Answer

a) \(a=e^2\) b) The only critical point is at \(x=e\); it is a local maximum for \(a>0\) and a local minimum for \(a<0\). All extrema lie on \(x=e\). c) \(m=a\)
53487112
A rational function has the form \(f(x)=\frac{ax^2+b}{x^2-1}\). The point \(P=(2,4)\) lies on the graph, and the slope there is \(f'(2)=-\frac{8}{3}\). Find \(a\) and \(b\).

Hints

- Use the point condition to obtain one equation in the parameters. - Use the quotient rule and the given tangent slope for a second equation. - Solve the resulting linear system only after simplifying the derivative condition.

Solution

1. Since \(P\) lies on the graph, \(4=\frac{4a+b}{3}\), so \(4a+b=12\). 2. By the quotient rule, \(f'(x)=\frac{2ax(x^2-1)-(ax^2+b)(2x)}{(x^2-1)^2}=\frac{-2x(a+b)}{(x^2-1)^2}\). 3. Use the slope condition: \(-\frac{8}{3}=f'(2)=-\frac{4(a+b)}{9}\), so \(a+b=6\). 4. Solving \(4a+b=12\) and \(a+b=6\) gives \(a=2\) and \(b=4\).

Answer

\(a=2\), \(b=4\)
53487212
A rational function has the form \(f(x)=\frac{ax^2+bx}{x+c}\). The graph has a vertical asymptote at \(x=-2\). At the x-intercept \(x=2\), the slope is \(f'(2)=0.5\). Find \(a\), \(b\), and \(c\), and write the complete function rule.

Hints

- Use the vertical asymptote to determine the denominator parameter. - Use the x-intercept to relate the numerator coefficients. - Apply the quotient rule and then impose the given slope at the intercept.

Solution

1. The vertical asymptote at \(x=-2\) requires \(-2+c=0\), so \(c=2\). 2. Since \(x=2\) is an x-intercept, \(4a+2b=0\), so \(b=-2a\). Thus \(f(x)=\frac{ax^2-2ax}{x+2}\). 3. By the quotient rule, \(f'(x)=\frac{(2ax-2a)(x+2)-(ax^2-2ax)}{(x+2)^2}=\frac{ax^2+4ax-4a}{(x+2)^2}\). 4. At \(x=2\), \(f'(2)=\frac{a}{2}\). Since \(f'(2)=0.5\), \(a=1\). 5. Therefore, \(b=-2\) and \(c=2\), giving \(f(x)=\frac{x^2-2x}{x+2}\).

Answer

\(a=1\), \(b=-2\), and \(c=2\); therefore, \(f(x)=\frac{x^2-2x}{x+2}\).
52575512
A circle has radius \(R\). For each integer \(n\ge3\), consider a regular \(n\)-gon inscribed in the circle and a regular \(n\)-gon circumscribed about the circle. a) Find formulas for the areas \(A_{i,n}\) of the inscribed polygon and \(A_{c,n}\) of the circumscribed polygon in terms of \(n\) and \(R\). b) Find \(\lim_{n\to\infty}A_{i,n}\) and \(\lim_{n\to\infty}A_{c,n}\). Use \(\lim_{x\to0}\frac{\sin x}{x}=1\). c) Use derivatives to describe and justify the monotonic behavior of both sequences as \(n\) increases.

Hints

- Divide each polygon into \(n\) congruent triangles from the center. - Use the radius and central angle to find each triangular area. - Apply sine and tangent in the relevant right triangles. - For monotonicity, use the quotient rule to differentiate \(\frac{\sin x}{x}\) and \(\frac{\tan x}{x}\), then determine the signs.

Solution

1. Divide the inscribed polygon into \(n\) isosceles triangles with side lengths \(R\) and central angle \(\frac{2\pi}{n}\). Each triangle has area \(\frac12R^2\sin\left(\frac{2\pi}{n}\right)\). Therefore, \(A_{i,n}=\frac n2R^2\sin\left(\frac{2\pi}{n}\right)\). 2. For the circumscribed polygon, \(R\) is the apothem. Each half-side has length \(R\tan\left(\frac{\pi}{n}\right)\), so each triangular section has area \(R^2\tan\left(\frac{\pi}{n}\right)\). Thus, \(A_{c,n}=nR^2\tan\left(\frac{\pi}{n}\right)\). 3. Rewrite the inscribed area as \(A_{i,n}=\pi R^2\frac{\sin(2\pi/n)}{2\pi/n}\). Since \(2\pi/n\to0\), \(A_{i,n}\to\pi R^2\). 4. Rewrite the circumscribed area as \(A_{c,n}=\pi R^2\frac{\tan(\pi/n)}{\pi/n}=\pi R^2\frac{\sin(\pi/n)}{(\pi/n)\cos(\pi/n)}\). Since \(\sin x/x\to1\) and \(\cos x\to1\), \(A_{c,n}\to\pi R^2\). 5. For \(f(x)=\frac{\sin x}{x}\), \(f'(x)=\frac{x\cos x-\sin x}{x^2}<0\) on \(0<x\le\frac{2\pi}{3}\). Because \(2\pi/n\) decreases as \(n\) increases, \(A_{i,n}\) is strictly increasing. 6. For \(g(x)=\frac{\tan x}{x}\), \(g'(x)=\frac{x\sec^2x-\tan x}{x^2}>0\) on \(0<x\le\frac{\pi}{3}\). Because \(\pi/n\) decreases as \(n\) increases, \(A_{c,n}\) is strictly decreasing.

Answer

a) \(A_{i,n}=\frac n2R^2\sin\left(\frac{2\pi}{n}\right)\) and \(A_{c,n}=nR^2\tan\left(\frac{\pi}{n}\right)\). b) Both sequences converge to \(\pi R^2\). c) For \(n\ge3\), \(A_{i,n}\) is strictly increasing and \(A_{c,n}\) is strictly decreasing.
52735112
Let \(f(x)=\frac{x^2+1}{(x-2)^3}\). 1. Identify the vertical asymptote and the multiplicity of the uncanceled denominator factor there. 2. Find \(f'(x)\) and show that the multiplicity of the uncanceled denominator factor at \(x=2\) increases from \(3\) to \(4\). 3. Let \(g(x)=\frac{u(x)}{(x-a)^n}\), where \(u\) is differentiable, \(u(a)\ne0\), and \(n\ge1\). Use the quotient rule to show that \(g'\) has an uncanceled denominator factor \((x-a)^{n+1}\).

Hints

- Track the power of the denominator factor after all cancellations, rather than assigning a special “order” name to the asymptote. - Factor powers of \(x-2\) before simplifying the derivative. - In the general case, evaluate the simplified numerator at \(x=a\) to decide whether cancellation is possible.

Solution

1. The denominator is zero at \(x=2\), while the numerator equals \(5\), so \(x=2\) is a vertical asymptote and the uncanceled denominator factor is \((x-2)^3\). 2. By the quotient rule, \(f'(x)=\frac{2x(x-2)^3-3(x^2+1)(x-2)^2}{(x-2)^6}\). Factoring and simplifying gives \(f'(x)=\frac{-x^2-4x-3}{(x-2)^4}\). 3. The numerator of \(f'\) equals \(-15\) at \(x=2\), so no further cancellation occurs. The denominator factor therefore has multiplicity \(4\). 4. For the general function, the quotient rule gives \(g'(x)=\frac{u'(x)(x-a)^n-nu(x)(x-a)^{n-1}}{(x-a)^{2n}}\). 5. Factoring and simplifying gives \(g'(x)=\frac{u'(x)(x-a)-nu(x)}{(x-a)^{n+1}}\). 6. At \(x=a\), the numerator equals \(-nu(a)\ne0\), so the denominator factor \((x-a)^{n+1}\) does not cancel.

Answer

1. Vertical asymptote: \(x=2\); denominator-factor multiplicity \(3\) 2. \(f'(x)=\frac{-x^2-4x-3}{(x-2)^4}\), with denominator-factor multiplicity \(4\) at \(x=2\) 3. \(g'(x)=\frac{u'(x)(x-a)-nu(x)}{(x-a)^{n+1}}\), and the factor \((x-a)^{n+1}\) is uncanceled because \(u(a)\ne0\)
52736012
Consider the family \(g_a(x)=\frac{a}{x^2+1}\), where \(a\ne0\). Show algebraically that the x-coordinates of the intersections of the graphs of \(g_a\) and \(g_a''\) are independent of \(a\).

Hints

- Use the quotient rule or negative-exponent form to differentiate. - Clear the denominators after canceling the nonzero parameter. - Use a substitution for the equation containing only even powers.

Solution

1. Differentiating twice gives \(g_a'(x)=\frac{-2ax}{(x^2+1)^2}\) and \(g_a''(x)=\frac{a(6x^2-2)}{(x^2+1)^3}\). 2. At an intersection, \(\frac{a}{x^2+1}=\frac{a(6x^2-2)}{(x^2+1)^3}\). 3. Since \(a\ne0\) and \(x^2+1>0\), simplify to \((x^2+1)^2=6x^2-2\), or \(x^4-4x^2+3=0\). 4. Let \(u=x^2\). Then \(u^2-4u+3=(u-1)(u-3)=0\), so \(x^2=1\) or \(x^2=3\). 5. Therefore, \(x=\pm1\) or \(x=\pm\sqrt{3}\), independent of \(a\).

Answer

\(x\in\{-\sqrt{3}, -1, 1, \sqrt{3}\}\)
52737412
Consider \(g_a(x) = \frac{ax + 4}{x + 2}\), where \(a \in \mathbb{R}\) and \(x \ne -2\). 1) Show that \(g_a'(x) = \frac{2a - 4}{(x + 2)^2}\). 2) Find the values of \(a\) for which \(g_a\) is strictly decreasing on each interval of its domain. 3) For those values of \(a\), find \(\lim_{x \to \infty} g_a(x)\). 4) Can a rational function of the form \(y = \frac{ax + b}{cx + d}\), where \(c \ne 0\), have \(\lim_{x \to \infty} y = \infty\) or \(\lim_{x \to -\infty} y = -\infty\)? Explain.

Hints

- Use the quotient rule. - The denominator of the derivative is a square. Determine when the numerator is negative. - Compare the leading terms to evaluate the limit at infinity. - For a linear-over-linear rational function, compare the degrees of the numerator and denominator.

Solution

1. Apply the quotient rule: \(g_a'(x) = \frac{a(x + 2) - (ax + 4)}{(x + 2)^2} = \frac{2a - 4}{(x + 2)^2}\). 2. For \(x \ne -2\), the denominator \((x + 2)^2\) is positive. Therefore, \(g_a'(x) < 0\) exactly when \(2a - 4 < 0\), or \(a < 2\). When \(a = 2\), the function is constant on its domain. 3. Divide the numerator and denominator by \(x\): \(\lim_{x \to \infty} \frac{a + 4/x}{1 + 2/x} = a\). 4. No. For any linear-over-linear rational function with \(c \ne 0\), the limits as \(x \to \pm\infty\) are both the finite value \(\frac{a}{c}\). Its end behavior approaches the horizontal asymptote \(y = \frac{a}{c}\), not positive or negative infinity.

Answer

1) \(g_a'(x) = \frac{2a - 4}{(x + 2)^2}\) 2) \(a < 2\) 3) \(\lim_{x \to \infty} g_a(x) = a\) 4) No. A linear-over-linear rational function approaches the finite horizontal asymptote \(y = \frac{a}{c}\).
52740812
Let \(h(x)=\frac{[u(x)]^2}{v(x)}\), where \(u\) and \(v\) are differentiable, \(u(x_0)=0\), and \(v(x_0)\ne 0\). Show algebraically that the graph of \(h\) always has a horizontal tangent at \(x=x_0\).

Hints

- Apply both the quotient rule and the chain rule. - Factor \(u(x)\) from the numerator of the derivative. - Substitute \(u(x_0)=0\) only after differentiating. - Use \(v(x_0)\ne 0\) to confirm the derivative is defined.

Solution

1. Apply the quotient rule and chain rule: \(h'(x)=\frac{2u(x)u'(x)v(x)-[u(x)]^2v'(x)}{[v(x)]^2}\). 2. Factor \(u(x)\) from the numerator: \(h'(x)=\frac{u(x)[2u'(x)v(x)-u(x)v'(x)]}{[v(x)]^2}\). 3. Evaluate at \(x=x_0\). Since \(u(x_0)=0\), \(h'(x_0)=\frac{0[2u'(x_0)v(x_0)-0\cdot v'(x_0)]}{[v(x_0)]^2}=0\). Because \(v(x_0)\ne 0\), the denominator is defined and nonzero. Therefore, the graph of \(h\) has a horizontal tangent at \(x=x_0\).

Answer

\(h'(x)=\frac{u(x)[2u'(x)v(x)-u(x)v'(x)]}{[v(x)]^2}\). Since \(u(x_0)=0\) and \(v(x_0)\ne 0\), \(h'(x_0)=0\), so the tangent is horizontal.
52949812
Let \(f(x)=\frac{u(x)}{v(x)}\), where \(u\) and \(v\) are polynomials of degrees \(n\) and \(m\), respectively. Assume \(n,m\ge 1\) and \(n\ne m\). 1. Determine the degrees of the two terms \(u'(x)v(x)\) and \(u(x)v'(x)\) in the numerator produced by the quotient rule. 2. Derive a formula for the degree \(k\) of the combined quotient-rule numerator \(u'v-uv'\). 3. Use your formula to show that \(k\ge n\).

Hints

- Recall how polynomial degrees behave under multiplication. - Determine how differentiation changes the degree of a nonconstant polynomial. - Compare the leading terms of \(u'v\) and \(uv'\). - Use the assumption \(n\ne m\) to decide whether those leading terms cancel.

Solution

1. Since \(u\) has degree \(n\), \(u'\) has degree \(n-1\). Therefore, \(\deg(u'v)=(n-1)+m=n+m-1\). Similarly, \(v'\) has degree \(m-1\), so \(\deg(uv')=n+(m-1)=n+m-1\). 2. Let \(a\) and \(b\) be the leading coefficients of \(u\) and \(v\). The leading terms of \(u'v\) and \(uv'\) are \(nabx^{n+m-1}\) and \(mabx^{n+m-1}\). Thus, the leading coefficient of \(u'v-uv'\) is \((n-m)ab\). Because \(n\ne m\), this coefficient is nonzero. Therefore, \(k=n+m-1\). 3. Since \(m\ge 1\), \(k-n=(n+m-1)-n=m-1\ge 0\). Hence, \(k\ge n\). This degree statement concerns the quotient-rule numerator before any common factor is canceled with the denominator.

Answer

1. Both terms have degree \(n+m-1\). 2. \(k=n+m-1\), because the leading coefficient is \((n-m)ab\ne 0\). 3. \(k-n=m-1\ge 0\), so \(k\ge n\).
53278312
The graph belongs to a rational function of the form \(f(x)=\frac{ax^2+bx}{x-d}\). The dashed line is a vertical asymptote. a) Read the vertical asymptote from the graph and find \(d\). b) Find \(a\) and \(b\), given that the graph crosses the x-axis at \(x=3\) and has slope \(\frac{3}{2}\) there. c) Write the complete function rule.
Figure for problem 532783

Hints

- The vertical asymptote identifies the denominator zero. - Use the x-intercept to relate \(a\) and \(b\). - Differentiate with the quotient rule and apply the given slope. - Solve the resulting equations one parameter at a time.

Solution

1. The vertical asymptote is \(x=1\), so \(d=1\). Thus, \(f(x)=\frac{ax^2+bx}{x-1}\). 2. Since \(f(3)=0\), the numerator is zero at \(x=3\): \(9a+3b=0\). Therefore, \(b=-3a\), and \(f(x)=\frac{a(x^2-3x)}{x-1}\). 3. Differentiate using the quotient rule: \(f'(x)=a\frac{(2x-3)(x-1)-(x^2-3x)}{(x-1)^2}=a\frac{x^2-2x+3}{(x-1)^2}\). 4. The slope condition gives \(f'(3)=\frac{3}{2}\). Since \(f'(3)=a\frac{9-6+3}{4}=\frac{3a}{2}\), it follows that \(a=1\). 5. Therefore, \(b=-3\), and \(f(x)=\frac{x^2-3x}{x-1}\).

Answer

a) \(d=1\) b) \(a=1\), \(b=-3\) c) \(f(x)=\frac{x^2-3x}{x-1}\)
53441812
Consider the family of functions \(f_k(x)=\frac{4x}{x^2+k}\), where \(x\ge0\) and \(k>0\). a) Find \(f_k'(x)\) using the quotient rule. b) Find the coordinates of the local maximum in terms of \(k\). c) The figure shows graphs p, q, and r for \(k\in\{1, 4, 9\}\). Match each graph to a value of \(k\) using part b. d) Find \(\lim_{x\to\infty}f_k(x)\) and explain whether it depends on \(k\). Method requirement: For every conclusion that a local extremum occurs, show the sign of the relevant first derivative on the two sides of the critical number and explicitly use the first derivative test. A critical-number calculation alone is not sufficient.
Figure for problem 534418

Hints

- Apply the quotient rule carefully. - Set the numerator of the derivative equal to zero. - Compare both coordinates of the maximum as \(k\) changes. - Compare the degrees of the numerator and denominator.

Solution

1. The quotient rule gives \(f_k'(x)=\frac{4(x^2+k)-8x^2}{(x^2+k)^2}=\frac{4k-4x^2}{(x^2+k)^2}\). 2. The derivative is zero at \(x=\sqrt{k}\). It changes from positive to negative, so this is a local maximum. Its value is \(f_k(\sqrt{k})=\frac{2}{\sqrt{k}}\), giving the local maximum \(\left(\sqrt{k}, \frac{2}{\sqrt{k}}\right)\). 3. As \(k\) increases, the maximum moves right and downward. Thus p corresponds to \(k=1\), q to \(k=4\), and r to \(k=9\). 4. The denominator has higher degree than the numerator, so \(\lim_{x\to\infty}f_k(x)=0\), independent of \(k\).

Answer

a) \(f_k'(x)=\frac{4k-4x^2}{(x^2+k)^2}\) b) \(\left(\sqrt{k}, \frac{2}{\sqrt{k}}\right)\) c) p: \(k=1\); q: \(k=4\); r: \(k=9\) d) \(0\), independent of \(k\)

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