Free math worksheets

- Recall how the imaginary unit is used to rewrite the square root of a negative number. - Keep both choices represented by the \(\pm\) sign when you rewrite the expression.

1. Since \(i^2=-1\), \(\sqrt{-9}=3i\). 2. Therefore, the two solutions are \(x=4+3i\) and \(x=4-3i\).

\(x=4+3i\) and \(x=4-3i\)

- Think about the relationship between nonreal roots of a polynomial whose coefficients are all real. - In a complex-conjugate pair, compare the real parts and the signs of the imaginary parts.

1. Nonreal solutions of a quadratic with real coefficients occur as a complex-conjugate pair. 2. The conjugate of \(-2+5i\) is \(-2-5i\), so that is the other solution.

\(-2-5i\)

- Look for the repeating cycle in the powers of \(i\). - Recall how to write the square root of a negative number using \(i\). - Use the quadratic formula.

1. The powers of \(i\) are \(i^1=i\), \(i^2=-1\), \(i^3=-i\), and \(i^4=1\). 2. Therefore, \(S=i-1-i+1=0\). 3. For \(x^2+4x+13=0\), the discriminant is \(4^2-4\cdot1\cdot13=-36\). 4. Since \(\sqrt{-36}=6i\), the quadratic formula gives \(x=\frac{-4\pm6i}{2}=-2\pm3i\).

a) \(S=0\) b) \(\{-2+3i, -2-3i\}\)

- Start from a factored quadratic whose factors correspond to the two given roots. - Relate the sum and product of the roots to the coefficients. - Use the fact that the two roots are complex conjugates when simplifying their sum and product.

1. Use the factored equation \((z-z_1)(z-z_2)=0\). Thus, \(b=-(z_1+z_2)\) and \(c=z_1z_2\). 2. The sum is \((2+i)+(2-i)=4\), so \(b=-4\). 3. The product is \((2+i)(2-i)=4-i^2=5\), so \(c=5\). 4. Therefore, the equation is \(z^2-4z+5=0\).

\(b=-4\), \(c=5\); the equation is \(z^2-4z+5=0\).

- For part a, compare the graph with the x-axis. - For part b, use the sign of the discriminant to connect the algebra with what the graph shows. - When a negative value appears under a square root, rewrite it using the imaginary unit.

1. The parabola does not intersect the x-axis, so the equation has no real solutions. 2. The discriminant is \((-4)^2-4(1)(8)=16-32=-16\). 3. The quadratic formula gives \(x=\frac{4\pm\sqrt{-16}}{2}=\frac{4\pm4i}{2}=2\pm2i\).

a) The graph has no x-intercepts, so the equation has no real solutions. b) \(x=2+2i\) and \(x=2-2i\)

- Determine when the imaginary part of \(z^2\) is zero. - Expand \((a+bi)^2\) and identify its two components. - A negative real square suggests a number on the imaginary axis. - Use \(i^2=-1\).

1. \(z^2=(a+bi)^2=a^2-b^2+2abi\). 2. The square is real exactly when its imaginary part is zero: \(2ab=0\). Thus, \(a=0\) or \(b=0\). 3. To solve \(z^2=-16\), the case \(b=0\) would require \(a^2=-16\), which has no real value of \(a\). 4. In the case \(a=0\), \(-b^2=-16\), so \(b=\pm4\). 5. Therefore, \(z=4i\) or \(z=-4i\).

a) \(a=0\) or \(b=0\) b) \(z\in\{4i, -4i\}\)

- Recall the conjugate-root theorem for polynomials with real coefficients. - Use the sum and product of the roots. - A negative discriminant gives nonreal roots.

1. Nonreal roots of a polynomial with real coefficients occur in conjugate pairs, so \(z_2=3+4i\). 2. By the relationships between roots and coefficients, \(p=-(z_1+z_2)=-6\). 3. Also, \(q=z_1z_2=(3-4i)(3+4i)=25\). 4. The discriminant is \(D=(-6)^2-4\cdot25=-64\). Since \(D<0\), the equation has no real solutions.

a) \(z_2=3+4i\) b) \(p=-6\) and \(q=25\) c) \(D=-64\), so there are no real solutions

- Use the quadratic formula and interpret a negative discriminant with the imaginary unit. - Compare the sum and product of the roots with the coefficients of the quadratic. - For part c, focus on how the real and imaginary parts of the two roots are related.

1. The quadratic formula gives \(z=\frac{4\pm\sqrt{16-52}}{2}=\frac{4\pm6i}{2}=2\pm3i\). 2. The sum is \((2+3i)+(2-3i)=4\). 3. The product is \((2+3i)(2-3i)=4+9=13\). 4. The two nonreal roots are complex conjugates: they have the same real part and opposite imaginary parts. Their sum and product are therefore real, consistent with the real coefficients of the quadratic.

a) \(z_1=2+3i\) and \(z_2=2-3i\) b) \(z_1+z_2=4\) and \(z_1z_2=13\) c) The roots are complex conjugates. Their imaginary parts cancel in the sum, and their product is real, which is consistent with a quadratic having real coefficients.

- The sign of the discriminant determines whether a real-coefficient quadratic has real or nonreal solutions. - Write the discriminant as an expression in \(m\) before solving an inequality. - The boundary between two nonreal solutions and real solutions occurs when the discriminant is zero.

1. The discriminant is \(D=(-6)^2-4(1)(m+10)=36-4m-40=-4m-4\). 2. Two nonreal complex solutions occur when \(D<0\). Thus, \(-4m-4<0\), which gives \(m>-1\). 3. When \(m=-1\), the discriminant is \(0\), so the equation has one repeated real solution. 4. Substituting \(m=-1\) gives \(x^2-6x+9=0=(x-3)^2\), so the repeated solution is \(x=3\).

a) \(m>-1\) b) When \(m=-1\), the equation has the repeated real solution \(x=3\).

- Distinguish between “no real solutions” and “no solutions over \(\mathbb{C}\).” - Rewrite the square root of a negative number using \(i\), and simplify the positive radical separately. - After applying the quadratic formula, simplify both the real and imaginary parts of each solution.

1. A negative discriminant means there are no real solutions, but complex solutions still exist. 2. The quadratic formula gives \(x=\frac{-6\pm\sqrt{-96}}{6}\). 3. Since \(\sqrt{-96}=4\sqrt{6}i\), \(x=\frac{-6\pm4\sqrt{6}i}{6}\). 4. Simplifying gives \(x=-1\pm\frac{2\sqrt{6}}{3}i\).

The error is concluding that a negative discriminant means no solutions at all; it means no real solutions. Over \(\mathbb{C}\), the solutions are \(x=-1+\frac{2\sqrt{6}}{3}i\) and \(x=-1-\frac{2\sqrt{6}}{3}i\).

- Expand the square and separate real and imaginary parts. - Set up two real equations by matching components. - Use one equation to eliminate a variable. - Reject values that cannot be squares of real numbers.

1. Expand: \((x+yi)^2=x^2-y^2+2xyi\). 2. Equating parts gives \(x^2-y^2=3\) and \(xy=2\). 3. Since \(x\ne0\), \(y=\frac{2}{x}\). Substitution gives \(x^2-\frac{4}{x^2}=3\). 4. Multiply by \(x^2\): \(x^4-3x^2-4=0\). Let \(u=x^2\), so \(u^2-3u-4=0\). 5. The values are \(u=4\) or \(u=-1\). Because \(u=x^2\ge0\), \(x^2=4\), so \(x=\pm2\). 6. Using \(xy=2\), the corresponding values are \(y=1\) when \(x=2\), and \(y=-1\) when \(x=-2\).

\((x, y)=(2, 1)\) or \((x, y)=(-2, -1)\)