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Area of triangles

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5355436
Use the measurements shown to find the area of the right triangle.
Figure for problem 535543

Hints

- Which two measurements in the diagram are needed to find a triangle's area? - How is a triangle's area related to a rectangle with the same base and height? - Check that you are using a perpendicular height.

Solution

1. The diagram shows a base of \(15\,\text{cm}\) and a perpendicular height of \(10\,\text{cm}\). 2. Use the triangle area formula: \(A=\frac{1}{2}bh\). 3. Substitute the measurements: \(A=\frac{1}{2}\times15\times10=75\,\text{cm}^2\).

Answer

The area is \(75\,\text{cm}^2\).
5109876
Triangle \(ABC\) has base \(AB=12\,\text{cm}\) and height \(5\,\text{cm}\). Point \(D\) lies on \(AB\) so that \(AD=3\,\text{cm}\). a) Without calculating the two triangle areas separately, determine \(\frac{A_{ADC}}{A_{ABC}}\). Explain why the common height makes this ratio depend only on the bases. b) Find the area of triangle \(ADC\).

Hints

- Compare the two bases before calculating either area. - What part of the triangle-area formula is identical for both triangles? - After finding the area ratio, use it with one triangle area.

Solution

1. Triangles \(ABC\) and \(ADC\) use bases on the same line \(AB\), so they have the same perpendicular height. 2. With the same height, the ratio of their areas equals the ratio of their bases: \(\frac{A_{ADC}}{A_{ABC}}=\frac{AD}{AB}=\frac{3}{12}=\frac{1}{4}\). 3. The area of triangle \(ABC\) is \(\frac{1}{2}\times12\times5=30\,\text{cm}^2\). 4. Therefore, \(A_{ADC}=\frac{1}{4}\times30=7.5\,\text{cm}^2\).

Answer

a) \(\frac{A_{ADC}}{A_{ABC}}=\frac{1}{4}\) b) \(A_{ADC}=7.5\,\text{cm}^2\)
5109996
Triangle \(ABC\) has base \(AB=10\,\text{cm}\) and corresponding height \(h=4\,\text{cm}\). A student claims, “If point \(C\) moves along a line parallel to \(AB\), the area of the triangle does not change.” a) Find the area of triangle \(ABC\). b) Explain why the student is correct. Which measurement in the area formula stays constant as \(C\) moves along the parallel line?

Hints

- What is the area formula for a triangle? - What is true about the distance between parallel lines? - How does the distance from \(C\) to the base affect the area?

Solution

1. The area is \(A=\frac{1}{2}bh=\frac{1}{2}\times10\times4=20\,\text{cm}^2\). 2. Every point on a line parallel to \(AB\) is the same perpendicular distance from \(AB\). 3. Therefore, both the base \(AB\) and the height remain constant, so the area remains \(20\,\text{cm}^2\).

Answer

a) \(20\,\text{cm}^2\) b) The height stays constant because the moving point remains on a line parallel to the base. Since the base also stays fixed, the area does not change.
5110756
A triangular sail has a base of \(4\,\text{m}\). Its other two sides are each about \(3\,\text{m}\) long. The height corresponding to the base is \(2.2\,\text{m}\). 1. Find the area of the sail. 2. Explain why the lengths of the other two sides are not needed when the corresponding height is known.

Hints

- Which measurements appear in the standard triangle area formula? - Imagine changing the other two side lengths while keeping the base and perpendicular height fixed. What happens to the area?

Solution

1. Use the \(4\,\text{m}\) side as the base: \(A=\frac{1}{2}\times4\times2.2=4.4\,\text{m}^2\). 2. A triangle's area is determined by a chosen base and the perpendicular height to that base. The other two sides affect the triangle's shape but do not appear in this area calculation.

Answer

1. \(4.4\,\text{m}^2\) 2. The area formula uses the base and its perpendicular height, so the other two side lengths are not needed.
5317206
Three figures, A, B, and C, are shown on a geoboard. The small gray square in the lower-right corner represents one square unit. a) Find the area of each figure in square units. Briefly explain how you found each area. b) Compare the three areas. What do you notice?
Figure for problem 531720

Hints

- For the rectangle, use length times width. - For the triangle, use one-half times the base times the height. - Split the step-shaped figure into smaller rectangles. - Compare the three numerical areas after you calculate them.

Solution

1. Figure A is a rectangle with width \(3\) units and height \(2\) units, so its area is \(3 \times 2 = 6\) square units. 2. Figure B is a right triangle with base \(4\) units and height \(3\) units. Its area is \(\frac{1}{2} \times 4 \times 3 = 6\) square units. 3. Figure C can be split into three vertical rectangles with areas \(3\), \(2\), and \(1\) square units. Its total area is \(3 + 2 + 1 = 6\) square units. 4. All three figures have the same area: \(6\) square units.

Answer

a) Figure A: \(6\) square units Figure B: \(6\) square units Figure C: \(6\) square units b) All three figures have the same area even though they have different shapes.
5317376
A square, a right triangle, and an L-shaped figure are shown on a geoboard. Which statement is true? - Figure A has a greater area than Figure B. - Figure B has a smaller area than Figure C. - All three figures have the same area. - Figure C has the greatest area. Justify your choice by finding the area of each figure. The gray square in the lower-right corner represents one square unit.
Figure for problem 531737

Hints

- Find the area of each figure separately. - Use one-half times the base times the height for the triangle. - Split the L-shaped figure into rectangles. - Compare the three results.

Solution

1. Figure A is a square with side length \(2\) units, so its area is \(2 \times 2 = 4\) square units. 2. Figure B is a right triangle with base \(4\) units and height \(2\) units, so its area is \(\frac{1}{2} \times 4 \times 2 = 4\) square units. 3. Figure C can be split into two nonoverlapping rectangles with areas \(2\) square units and \(2\) square units, so its total area is \(2 + 2 = 4\) square units. 4. Therefore, all three figures have the same area.

Answer

All three figures have the same area: \(4\) square units each.
5317546
Two figures are shown on a geoboard. The small gray square in the lower-right corner represents one unit square. Find the area of Figures A and B in square units.
Figure for problem 531754

Hints

- Use length times width for the rectangle. - For the triangle, imagine a rectangle with the same base and height. - What fraction of that rectangle is the triangle?

Solution

1. Figure A is a \(4 \times 2\) rectangle, so its area is \(4 \times 2 = 8\) square units. 2. Figure B is a triangle with base \(4\) units and height \(2\) units, so its area is \(\frac{1}{2} \times 4 \times 2 = 4\) square units.

Answer

Figure A has an area of \(8\) square units, and Figure B has an area of \(4\) square units.
5352036
Look at rectangle a) and triangle b) on the geoboard. Which figure has the greater area, or are their areas equal? Justify your answer without counting the unit squares one at a time.
Figure for problem 535203

Hints

- Use length times width for the rectangle. - Imagine completing the triangle to make a rectangle. - What fraction of that rectangle is the triangle?

Solution

1. Rectangle a) has side lengths \(4\) units and \(1\) unit, so its area is \(4 \times 1 = 4\) square units. 2. Triangle b) has base \(2\) units and height \(4\) units, so its area is \(\frac{1}{2} \times 2 \times 4 = 4\) square units. 3. The two figures have equal areas.

Answer

The two figures have the same area: \(4\) square units each.
5352056
Which three figures have the same area? Give the letters of those figures. The small gray square in the lower-right corner represents one square unit.
Figure for problem 535205

Hints

- Find the area of each figure separately. - For each triangle, use one-half times the base times the height. - Compare all four results.

Solution

1. Figure a) is a \(2 \times 2\) square, so its area is \(4\) square units. 2. Figure b) is a \(4 \times 1\) rectangle, so its area is \(4\) square units. 3. Figure c) is a triangle with base \(3\) units and height \(2\) units, so its area is \(\frac{1}{2} \times 3 \times 2 = 3\) square units. 4. Figure d) is a triangle with base \(4\) units and height \(2\) units, so its area is \(\frac{1}{2} \times 4 \times 2 = 4\) square units. 5. Figures a), b), and d) have the same area.

Answer

Figures a), b), and d) have the same area: \(4\) square units each.
5352636
Find the area of each triangle on the geoboard. Compare the results. Which triangle covers more area?
Figure for problem 535263

Hints

- Use the triangle area formula with a base and its corresponding height. - Count the spaces between pegs to determine lengths. - For triangle a), the two sides that form the right angle can be used as the base and height.

Solution

1. Triangle a) is a right triangle with perpendicular side lengths \(4\) units and \(5\) units. Its area is \(A_a=\frac{1}{2}\times4\times5=10\) square units. 2. Triangle b) has a base of \(5\) units and a height of \(4\) units. Its area is \(A_b=\frac{1}{2}\times5\times4=10\) square units. 3. The areas are equal, so neither triangle covers more area.

Answer

Both triangles have an area of \(10\) square units, so neither is larger.
5354196
Find the area of the triangle on the geoboard. Give your answer as a decimal in square centimeters. Each grid square represents \(1\,\text{cm}^2\).
Figure for problem 535419

Hints

- Use the grid to identify a base and its corresponding perpendicular height. - Substitute those measurements into the triangle area relationship. - Convert your final area to a decimal only after you have found it exactly.

Solution

1. The horizontal base is \(5\,\text{cm}\) long. 2. The corresponding height is \(3\,\text{cm}\). 3. The area is \(A=\frac{1}{2}\times5\times3=7.5\,\text{cm}^2\).

Answer

The area is \(7.5\,\text{cm}^2\).
5354246
What is the area of the right triangle? Each grid square is \(1\,\text{cm}\) by \(1\,\text{cm}\). Do not use the triangle-area formula. Explain how completing the figure to a rectangle shows the triangle's area.
Figure for problem 535424

Hints

- Imagine adding a matching right triangle to complete a rectangle. - How are the two triangles related inside that rectangle? - Use the rectangle's dimensions after explaining the one-half relationship.

Solution

1. Complete the triangle to a \(7\,\text{cm}\times3\,\text{cm}\) rectangle. 2. A diagonal divides that rectangle into two congruent right triangles, so the shown triangle is exactly half of the rectangle. 3. The rectangle area is \(7\times3=21\,\text{cm}^2\). 4. The triangle area is \(21\div2=10.5\,\text{cm}^2\).

Answer

The triangle is half of a \(7\,\text{cm}\times3\,\text{cm}\) rectangle, so its area is \(10.5\,\text{cm}^2\).
5355426
Imagine completing the right triangle to form the rectangle shown. Find the area of the triangle.
Figure for problem 535542

Hints

- How many congruent right triangles make the completed rectangle? - Read the rectangle's dimensions from the diagram and find its area first. - Divide that area by the number of congruent triangles.

Solution

1. The completed rectangle has area \(8\times5=40\,\text{cm}^2\). 2. The right triangle is half of that rectangle, so its area is \(40\div2=20\,\text{cm}^2\).

Answer

\(20\,\text{cm}^2\)
5358366
A triangle has an area of \(30\,\text{cm}^2\). Its base is labeled in the diagram. Find the corresponding height.
Figure for problem 535836

Hints

- Read the base length from the diagram. - Substitute the known area and base into the triangle area relationship. - Rearrange the equation so the unknown height is alone.

Solution

1. Use \(A=\frac{1}{2}bh\): \(30=\frac{1}{2}\times12\times h=6h\). 2. Divide by \(6\): \(h=30\div6=5\,\text{cm}\).

Answer

The height is \(5\,\text{cm}\).
5365966
Find the area of triangle \(ABC\). Use the measurements shown.
Figure for problem 536596

Hints

- Which side is shown as the base? - Recall the triangle area formula. - Use the height that is perpendicular to the chosen base.

Solution

1. The base is \(8\,\text{cm}\), and its corresponding height is \(4\,\text{cm}\). 2. The area is \(A=\frac{1}{2}\times8\times4=16\,\text{cm}^2\).

Answer

The area of the triangle is \(16\,\text{cm}^2\).
5370256
In triangle \(ABC\), point \(M\) is the midpoint of \(\overline{BC}\). Triangle \(ABM\) has area \(18\,\text{cm}^2\). Find the area of triangle \(ABC\).
Figure for problem 537025

Hints

- What does it mean for \(M\) to be the midpoint of \(\overline{BC}\)? - Compare the bases \(BM\) and \(MC\) and the heights of the two smaller triangles. - How can the two smaller triangle areas be combined to get the whole triangle?

Solution

1. Because \(M\) is the midpoint of \(\overline{BC}\), triangles \(ABM\) and \(ACM\) have equal base lengths and the same height from \(A\) to line \(BC\). 2. Therefore, the two smaller triangles have equal areas. 3. The total area is \(18+18=36\,\text{cm}^2\).

Answer

Triangle \(ABC\) has area \(36\,\text{cm}^2\).
5372396
A shaded triangle is drawn inside a rectangle. One side of the triangle is a full side of the rectangle, and the opposite vertex lies on the opposite side of the rectangle. The triangle has area \(14\,\text{cm}^2\). Find the area of the rectangle.
Figure for problem 537239

Hints

- Compare the triangle with the entire rectangle. - Use the area formulas for a triangle and a rectangle with the same base and height. - Imagine making a congruent copy of the triangle. - Decide how many triangle areas make the rectangle area.

Solution

1. The triangle and rectangle have the same base and height. 2. A triangle with the same base and height as a rectangle has half the rectangle area. 3. Therefore, the rectangle area is \(2 \times 14=28\,\text{cm}^2\).

Answer

\(28\,\text{cm}^2\)
5109916
Two triangles have the same area. The first triangle has a base of \(10\,\text{cm}\) and a height of \(6\,\text{cm}\). The second triangle's base is half as long as the first triangle's base. a) Find the area of each triangle. b) Find the height of the second triangle. c) Explain how a triangle's height must change when its base is halved but its area stays the same.

Hints

- First find the area shared by both triangles. - How long is the second triangle's base? - Use the triangle area formula to find the missing height. - Compare the two base-height pairs.

Solution

1. The first triangle has area \(A=\frac{1}{2}\times10\times6=30\,\text{cm}^2\). 2. The second triangle's base is \(10\div2=5\,\text{cm}\). 3. Set its area equal to \(30\): \(30=\frac{1}{2}\times5\times h_2=2.5h_2\). Thus, \(h_2=30\div2.5=12\,\text{cm}\). 4. When the base is halved, the height must double to keep the product of base and height constant.

Answer

a) \(30\,\text{cm}^2\) b) \(12\,\text{cm}\) c) The height must double.
5110056
A triangle has a perimeter of \(32\,\text{cm}\). Two of its sides are each \(10\,\text{cm}\) long. The triangle's area is \(48\,\text{cm}^2\). Find the length of the third side and the height corresponding to that side.

Hints

- How are the perimeter and the three side lengths related? - What is the area formula for a triangle? - Which side should be used as the base to find the requested height?

Solution

1. The third side has length \(32-10-10=12\,\text{cm}\). 2. Let \(h\) be the height to the \(12\,\text{cm}\) side. From \(48=\frac{1}{2}\times12\times h\), \(48=6h\). 3. Therefore, \(h=48\div6=8\,\text{cm}\).

Answer

The third side is \(12\,\text{cm}\) long, and its corresponding height is \(8\,\text{cm}\).
5110066
A triangular sail has a base of \(1.2\,\text{m}\) and a corresponding height of \(80\,\text{cm}\). A second sail has the same area but has a base of \(1.5\,\text{m}\). Find the second sail's height in centimeters.

Hints

- First express the measurements in compatible units. - Equal areas can be represented by an equation. - Find the first sail's area before solving for the missing height. - Convert the final height to centimeters.

Solution

1. Convert the first sail's height to meters: \(80\,\text{cm}=0.8\,\text{m}\). 2. The first sail has area \(A=\frac{1}{2}\times1.2\times0.8=0.48\,\text{m}^2\). 3. For the second sail, \(0.48=\frac{1}{2}\times1.5\times h=0.75h\). 4. Therefore, \(h=0.48\div0.75=0.64\,\text{m}=64\,\text{cm}\).

Answer

The second sail's height is \(64\,\text{cm}\).
5110076
A triangle has perimeter \(24\,\text{cm}\). One side is \(10\,\text{cm}\) long, and its corresponding height is \(4.8\,\text{cm}\). The height corresponding to a second side is \(8\,\text{cm}\). Find the lengths of the second side and the remaining side.

Hints

- A triangle's area can be found using any side and its corresponding height. - The area is the same no matter which base-height pair you use. - Once two side lengths are known, use the perimeter to find the third.

Solution

1. Use the \(10\,\text{cm}\) side and its corresponding height to find the area: \(A=\frac{1}{2}\times10\times4.8=24\,\text{cm}^2\). 2. Let \(x\) be the side whose corresponding height is \(8\,\text{cm}\). Then \(24=\frac{1}{2}\times x\times8=4x\), so \(x=6\,\text{cm}\). 3. Let \(y\) be the remaining side. Use the perimeter: \(y=24-6-10=8\,\text{cm}\).

Answer

The second side is \(6\,\text{cm}\), and the remaining side is \(8\,\text{cm}\).
5110556
A square playground with side length \(12\,\text{m}\) will be replaced by a triangular green space with exactly the same area. The triangle must have a base of \(16\,\text{m}\). Find the required height of the triangle.

Hints

- Find the area of the square first. - Equal-area figures have the same numerical area. - Substitute the known base and area into the triangle area formula. - Solve the resulting equation for the height.

Solution

1. The square's area is \(12\times12=144\,\text{m}^2\). 2. The triangle must also have area \(144\,\text{m}^2\), so \(144=\frac{1}{2}\times16\times h\). 3. Simplify to \(144=8h\), then divide: \(h=144\div8=18\,\text{m}\).

Answer

The triangle must have a height of \(18\,\text{m}\).
5110576
Mia and Leo draw triangles. Mia's triangle has a base of \(10\,\text{cm}\) and a height of \(6\,\text{cm}\). Leo's triangle has twice the base length but half the height. a) Find both areas and compare them. b) Leo draws a third triangle with the same \(20\,\text{cm}\) base as his second triangle. Its area should be four times Mia's triangle's area. What height must the third triangle have?

Hints

- Use the triangle area formula. - Find Leo's base and height before calculating his area. - What happens when one factor doubles and the other is halved? - In part b), substitute the target area and solve for the height.

Solution

1. Mia's triangle has area \(A_M=\frac{1}{2}\times10\times6=30\,\text{cm}^2\). 2. Leo's second triangle has base \(20\,\text{cm}\) and height \(3\,\text{cm}\), so \(A_L=\frac{1}{2}\times20\times3=30\,\text{cm}^2\). The areas are equal. 3. The third triangle needs area \(4\times30=120\,\text{cm}^2\). 4. Solve \(120=\frac{1}{2}\times20\times h=10h\). Thus, \(h=12\,\text{cm}\).

Answer

a) Both areas are \(30\,\text{cm}^2\). b) The height must be \(12\,\text{cm}\).
5110686
A sailing club will replace a triangular sail with a rectangular sail of the same area. The triangular sail has a base of \(5.40\,\text{m}\) and a height of \(3.50\,\text{m}\). The rectangular sail will be \(4.20\,\text{m}\) long. Find the width of the rectangular sail.

Hints

- Find the area of the triangular sail first. - The replacement sail must have the same area. - Divide the rectangle's area by its known length.

Solution

1. The triangular sail has area \(\frac{1}{2}\times5.40\times3.50=9.45\,\text{m}^2\). 2. The rectangle must have the same area, so its width is \(9.45\div4.20=2.25\,\text{m}\).

Answer

The rectangular sail must be \(2.25\,\text{m}\) wide.
5110696
A gardener compares two lawns. Lawn A is a right triangle with perpendicular side lengths \(18\,\text{m}\) and \(12\,\text{m}\). Lawn B is a rectangle with the same area, and one side of the rectangle is also \(12\,\text{m}\). Find the rectangle's other side length. Explain how you can find it without first calculating either area.

Hints

- Compare the area formulas for a triangle and a rectangle. - One side length is the same in both figures. - Picture two congruent copies of the triangle forming a rectangle.

Solution

1. A triangle has half the area of a rectangle with the same base and height. 2. Since both figures have a \(12\,\text{m}\) side, the rectangle's other side must be half of \(18\,\text{m}\) to have the same area. 3. Therefore, the missing side length is \(18\div2=9\,\text{m}\).

Answer

The rectangle's other side is \(9\,\text{m}\). The factor \(\frac{1}{2}\) in the triangle area formula means the corresponding rectangle side must be half as long when the shared side is unchanged.
5110706
A triangular stage for a school festival has a base of \(15\,\text{m}\) and a height of \(6.40\,\text{m}\). The plan changes so that the stage area will be doubled. The new stage will be rectangular and \(12\,\text{m}\) long. Find the required width of the new stage.

Hints

- Find the area of the original triangular stage. - Apply the required change to the area before working with the rectangle. - Divide the new area by the rectangle's known length.

Solution

1. The original stage has area \(\frac{1}{2}\times15\times6.40=48\,\text{m}^2\). 2. Doubling the area gives \(2\times48=96\,\text{m}^2\). 3. The rectangle's width is \(96\div12=8\,\text{m}\).

Answer

The new rectangular stage must be \(8\,\text{m}\) wide.
5110786
A triangle has a base of \(10\,\text{cm}\) and a corresponding height of \(4\,\text{cm}\). a) Find its area. b) The opposite vertex is moved sideways until the triangle has an obtuse angle, but the height remains \(4\,\text{cm}\). Does the area change? Explain. c) In the new obtuse triangle, how many of the three altitudes lie outside the triangle?

Hints

- Which measurements determine a triangle's area? - Does the area formula include the horizontal position of the opposite vertex or the angle type? - Recall where the altitudes lie in an obtuse triangle.

Solution

1. The area is \(A=\frac{1}{2}\times10\times4=20\,\text{cm}^2\). 2. Moving the vertex sideways does not change the base or its corresponding height, so the area remains \(20\,\text{cm}^2\). 3. An obtuse triangle has exactly two altitudes outside the triangle.

Answer

a) \(20\,\text{cm}^2\) b) No. The base and corresponding height are unchanged, so the area is unchanged. c) Two altitudes lie outside the triangle.
5110796
A right triangle has legs of \(5\,\text{cm}\) and \(12\,\text{cm}\). Its hypotenuse is \(13\,\text{cm}\). a) Explain why each leg can serve as the height corresponding to the other leg. Give both of these heights. b) Find the area of the triangle. c) Find the height drawn to the hypotenuse. Round to the nearest hundredth.

Hints

- What does the right angle tell you about the two legs and their corresponding heights? - Use the area you found to write a second area equation with the hypotenuse as the base. - Rearrange the triangle area formula to solve for a height.

Solution

1. The legs are perpendicular. Therefore, the height corresponding to the \(5\,\text{cm}\) leg is \(12\,\text{cm}\), and the height corresponding to the \(12\,\text{cm}\) leg is \(5\,\text{cm}\). 2. The area is \(A=\frac{1}{2}\times5\times12=30\,\text{cm}^2\). 3. Let \(h\) be the height drawn to the hypotenuse. Using the hypotenuse as the base, \(30=\frac{1}{2}\times13\times h\). Thus, \(h=\frac{60}{13}\,\text{cm}\approx4.62\,\text{cm}\).

Answer

a) The two heights are \(12\,\text{cm}\) and \(5\,\text{cm}\), respectively. b) \(30\,\text{cm}^2\) c) \(\approx4.62\,\text{cm}\)
5110886
Triangles A and B each have area \(24\,\text{cm}^2\). a) Triangle A has a base of \(8\,\text{cm}\). Find its height. b) Triangle B has a height of \(4\,\text{cm}\). Find its base. c) A student claims, “If a triangle's base is doubled and its corresponding height is halved, its area always stays the same.” Decide whether the claim is always true. Use the triangle-area formula with a general base \(b\) and height \(h\) to justify your answer.

Hints

- Use the triangle-area relationship to recover each missing measurement. - For the general claim, represent the original base and height by letters. - Compare the original area expression with the expression after both changes.

Solution

1. For triangle A, \(24=\frac{1}{2}\times8\times h=4h\), so \(h=6\,\text{cm}\). 2. For triangle B, \(24=\frac{1}{2}\times b\times4=2b\), so \(b=12\,\text{cm}\). 3. A triangle with base \(b\) and corresponding height \(h\) has area \(A=\frac{1}{2}bh\). 4. After doubling the base and halving the height, the area is \(\frac{1}{2}(2b)\left(\frac{h}{2}\right)=\frac{1}{2}bh=A\). 5. Therefore, the claim is always true.

Answer

a) \(6\,\text{cm}\) b) \(12\,\text{cm}\) c) The claim is always true because \(\frac{1}{2}(2b)\left(\frac{h}{2}\right)=\frac{1}{2}bh\).
5110976
A triangle has base \(12\,\text{cm}\) and corresponding height \(4\,\text{cm}\). a) Find its area. b) Check the statement: “If the base is halved and the height is doubled, the triangle's area stays the same.” c) The base is reduced to one-third of its original length. What height is needed for the new area to be twice the original area?

Hints

- What happens to a product when one factor is divided by \(2\) and the other is multiplied by \(2\)? - Find the new target area and new base separately. - Write an equation for the unknown height.

Solution

1. The original area is \(A=\frac{1}{2}\times12\times4=24\,\text{cm}^2\). 2. The changed measurements are a \(6\,\text{cm}\) base and an \(8\,\text{cm}\) height. The area is \(\frac{1}{2}\times6\times8=24\,\text{cm}^2\), so the statement is true. 3. The new base in part c) is \(12\div3=4\,\text{cm}\), and the target area is \(2\times24=48\,\text{cm}^2\). 4. Solve \(48=\frac{1}{2}\times4\times h=2h\). Thus, \(h=24\,\text{cm}\).

Answer

a) \(24\,\text{cm}^2\) b) The statement is true. c) \(24\,\text{cm}\)
5114086
A triangle must have an area of exactly \(15\,\text{cm}^2\). a) Find the height when the base is \(6\,\text{cm}\). b) Give another base-height pair that produces the same area. c) If two triangles have the same area and the same base, must they have exactly the same shape? Explain.

Hints

- Rearrange the area formula to find a missing height. - Find two positive numbers whose product is twice the area. - Imagine moving the third vertex left or right without changing its distance from the base.

Solution

1. Use \(A=\frac{1}{2}bh\): \(15=\frac{1}{2}\times6\times h=3h\), so \(h=5\,\text{cm}\). 2. Any positive base-height pair with product \(30\,\text{cm}^2\) works. For example, \(b=10\,\text{cm}\) and \(h=3\,\text{cm}\). 3. The triangles do not have to have the same shape. The third vertex can move along a line parallel to the base, changing side lengths and angles while keeping the height and area fixed.

Answer

a) \(5\,\text{cm}\) b) One possible pair is \(10\,\text{cm}\) and \(3\,\text{cm}\). c) No. The third vertex can move parallel to the base without changing the height or area.
5116946
A right triangle has legs \(6\,\text{cm}\) and \(8\,\text{cm}\) and hypotenuse \(10\,\text{cm}\). a) Find the area. b) Find the height corresponding to the \(10\,\text{cm}\) hypotenuse. c) What happens to the area if the \(6\,\text{cm}\) leg is doubled while the \(8\,\text{cm}\) leg stays the same? Explain without drawing a new diagram.

Hints

- How can the perpendicular legs be used as a base and height? - Any side can be a base if you use its corresponding height. - What happens to a product when one factor doubles?

Solution

1. The legs are perpendicular, so \(A=\frac{1}{2}\times6\times8=24\,\text{cm}^2\). 2. Let \(h\) be the height corresponding to the hypotenuse. Then \(24=\frac{1}{2}\times10\times h=5h\), so \(h=4.8\,\text{cm}\). 3. If the \(6\,\text{cm}\) leg doubles while the other leg stays fixed, one factor in \(\frac{1}{2}bh\) doubles. Therefore, the area doubles to \(48\,\text{cm}^2\).

Answer

a) \(24\,\text{cm}^2\) b) \(4.8\,\text{cm}\) c) The area doubles to \(48\,\text{cm}^2\).
5117066
Two identical rectangles each measure \(10\,\text{cm}\times6\,\text{cm}\). Rectangle A is divided by a segment from one corner to the midpoint of the opposite long side. Rectangle B is divided by a segment from one corner to the midpoint of the opposite short side. Each segment creates a right triangle. Compare the areas of the two triangles and justify your conclusion.

Hints

- Find each triangle's area separately. - Identify which rectangle side is halved in each case. - Compare the two base-height products.

Solution

1. In Rectangle A, the triangle has base \(5\,\text{cm}\) and height \(6\,\text{cm}\). Its area is \(\frac{1}{2}\times5\times6=15\,\text{cm}^2\). 2. In Rectangle B, the triangle has base \(3\,\text{cm}\) and height \(10\,\text{cm}\). Its area is \(\frac{1}{2}\times3\times10=15\,\text{cm}^2\). 3. The triangles have equal areas because the base-height products are equal: \(5\times6=3\times10=30\).

Answer

Both triangles have area \(15\,\text{cm}^2\). Their shapes differ, but their base-height products are equal.
5117096
A triangle has area \(24\,\text{cm}^2\) and base \(8\,\text{cm}\). a) Find its corresponding height. b) Find the area if the base is halved to \(4\,\text{cm}\) while the height stays the same. c) Find the area if the original \(8\,\text{cm}\) base stays the same and the height is tripled to \(18\,\text{cm}\).

Hints

- First use the triangle area formula to find the missing height. - How does halving or tripling one factor affect a product? - You may calculate directly or use proportional reasoning.

Solution

1. Solve \(24=\frac{1}{2}\times8\times h=4h\), giving \(h=6\,\text{cm}\). 2. With base \(4\,\text{cm}\), the area is \(\frac{1}{2}\times4\times6=12\,\text{cm}^2\). 3. With height \(18\,\text{cm}\), the area is \(\frac{1}{2}\times8\times18=72\,\text{cm}^2\).

Answer

a) \(6\,\text{cm}\) b) \(12\,\text{cm}^2\) c) \(72\,\text{cm}^2\)
5118756
A triangle has side lengths \(14\,\text{cm}\) and \(10\,\text{cm}\). The height corresponding to the \(14\,\text{cm}\) side is \(5\,\text{cm}\). a) Find the area. b) Find the height corresponding to the \(10\,\text{cm}\) side. c) Explain why the triangle's area is the same no matter which side is chosen as the base.

Hints

- Which base already has a known corresponding height? - How are base, height, and area related? - Can one fixed triangle have two different areas?

Solution

1. The area is \(A=\frac{1}{2}\times14\times5=35\,\text{cm}^2\). 2. Let \(h\) be the height corresponding to the \(10\,\text{cm}\) side. Then \(35=\frac{1}{2}\times10\times h=5h\). Thus, \(h=7\,\text{cm}\). 3. The triangle itself does not change when a different side is chosen as the base. Each base must be paired with its own perpendicular height, and every valid pair gives the same enclosed area.

Answer

a) \(35\,\text{cm}^2\) b) \(7\,\text{cm}\) c) Choosing a different base does not change the triangle; the corresponding height adjusts so the area remains the same.
5352626
Find the area of the triangle in square units by enclosing it in the smallest rectangle whose sides follow the geoboard grid. Show how the outside triangular regions are subtracted.
Figure for problem 535262

Hints

- Find a rectangle that exactly encloses the triangle. - Calculate the areas outside the triangle but inside the rectangle. - Subtract those areas from the rectangle area.

Solution

1. Enclose the triangle in a \(6 \times 4\) rectangle with area \(24\) square units. 2. The left outside triangle has area \(\frac{1}{2} \times 2 \times 4=4\) square units. The right outside triangle has area \(\frac{1}{2} \times 4 \times 4=8\) square units. 3. The triangle area is \(24-4-8=12\) square units.

Answer

\(12\) square units
5355446
A glass plate is shaped like the right trapezoid shown. The dashed segment splits it into a rectangle and a right triangle. Find only the area of the triangle.
Figure for problem 535544

Hints

- Use the two parallel-side labels to determine the triangle's horizontal base. - The dashed segment shows that the triangle has the same perpendicular height as the trapezoid. - Apply the triangle area relationship to those two measurements.

Solution

1. The triangle's base is \(100-70=30\,\text{cm}\). 2. Its height is the trapezoid's height, \(40\,\text{cm}\). 3. The area is \(\frac{1}{2}\times30\times40=600\,\text{cm}^2\).

Answer

The triangle has area \(600\,\text{cm}^2\).
5365986
Use the diagram to find the area of obtuse triangle \(PQR\).
Figure for problem 536598

Hints

- Which segment in the diagram is perpendicular to the line containing the base? - The height of an obtuse triangle can lie outside the triangle. - Which two diagram measurements determine the area?

Solution

1. The diagram shows base \(QR=5\,\text{cm}\) and a perpendicular height of \(6\,\text{cm}\) drawn to the line containing the base. 2. The area formula still applies: \(A=\frac{1}{2}\times5\times6=15\,\text{cm}^2\).

Answer

The area of the triangle is \(15\,\text{cm}^2\).
5365996
Find the area of the shaded triangle on the grid. Each grid-cell side represents \(1\,\text{cm}\).
Figure for problem 536599

Hints

- Count the grid cells along the horizontal side. - Count the perpendicular distance from the opposite vertex to the base line. - Use the triangle area formula.

Solution

1. The horizontal base is \(3\,\text{cm}\) long. 2. The perpendicular height is \(3\,\text{cm}\). 3. The area is \(A=\frac{1}{2}\times3\times3=4.5\,\text{cm}^2\).

Answer

The area of the triangle is \(4.5\,\text{cm}^2\).
5370146
In triangle \(ABC\), point \(D\) lies on side \(BC\). Given \(BD=3\,\text{cm}\) and \(BC=10\,\text{cm}\), find the ratio of the area of \(\triangle ABD\) to the area of \(\triangle ADC\).
Figure for problem 537014

Hints

- Find \(DC\) from the total length \(BC\). - Do the two triangles have the same height to line \(BC\)?

Solution

1. Find the remaining segment: \(DC=10-3=7\,\text{cm}\). 2. The two triangles have the same perpendicular height to line \(BC\), so their areas are proportional to their bases. 3. Therefore, the ratio is \(\frac{BD}{DC}=\frac{3}{7}\).

Answer

The ratio of the area of \(\triangle ABD\) to the area of \(\triangle ADC\) is \(\frac{3}{7}\).
5541116
The diagram shows a parallelogram made from two congruent copies of the same triangle. Its base is \(b\) and its perpendicular height is \(h\). Without using the triangle-area formula, explain why the area of one of the triangles is \(\frac{1}{2}bh\).
Figure for problem 554111

Hints

- Compare the two triangular pieces inside the parallelogram. - What fraction of the parallelogram belongs to one triangle? - Express the parallelogram's area using its labeled base and perpendicular height before taking that fraction.

Solution

1. The diagonal separates the parallelogram into the two congruent triangle copies, so the two triangles have equal area and together make the entire parallelogram. 2. A parallelogram with base \(b\) and perpendicular height \(h\) has area \(bh\). 3. Because each congruent triangle is one half of the parallelogram, one triangle has area \(\frac{1}{2}bh\). 4. Any triangle can be copied and paired in this way, so the argument gives the general triangle-area relationship.

Answer

The two congruent triangles exactly make a parallelogram of area \(bh\). Each triangle is half of that area, so \(A=\frac{1}{2}bh\).
5109776
Lucas wants to construct a triangle with area \(20\,\text{cm}^2\). He chooses a base of \(8\,\text{cm}\) and requires one of the sides adjacent to that base to be \(4\,\text{cm}\). Use a calculation to explain why such a triangle cannot be constructed.

Hints

- First calculate the height needed to produce the required area. - Compare a triangle's height with the sides that connect the opposite vertex to the base. - Can an adjacent side be shorter than the perpendicular distance to the base line?

Solution

1. Let \(h\) be the height to the \(8\,\text{cm}\) base. From \(A=\frac{1}{2}bh\), \(20=\frac{1}{2}\times8\times h\). 2. This gives \(20=4h\), so \(h=5\,\text{cm}\). 3. The perpendicular distance from the opposite vertex to the base line cannot be longer than a segment from that vertex to an endpoint of the base. 4. Because the required height is \(5\,\text{cm}\) but the specified adjacent side is only \(4\,\text{cm}\), the triangle is impossible.

Answer

The required height is \(5\,\text{cm}\). Since an adjacent side is only \(4\,\text{cm}\), it cannot reach a point that is \(5\,\text{cm}\) from the base line. Therefore, the triangle cannot be constructed.
5512586
Triangle A has a base of \(14\,\text{cm}\) and a height of \(6\,\text{cm}\). Triangle B has the same area as triangle A. Its base and height are whole numbers of centimeters, and its base is exactly \(5\,\text{cm}\) longer than its height. Find the base and height of triangle B. Explain why your pair is the only whole-number pair that works.

Hints

- Equal triangle areas impose a condition on the products of their bases and corresponding heights. - The whole-number condition suggests organizing possible factor pairs rather than guessing randomly. - Use the stated difference between base and height to select among the possible pairs.

Solution

1. Triangle A has area \(\frac{1}{2}\times14\times6=42\,\text{cm}^2\). 2. For triangle B to have the same area, its base-height product must be \(84\), because \(\frac{1}{2}bh=42\). 3. Check whole-number factor pairs of \(84\): \(1\times84\), \(2\times42\), \(3\times28\), \(4\times21\), \(6\times14\), and \(7\times12\). 4. Only \(7\) and \(12\) differ by \(5\). Since the base is longer, the height is \(7\,\text{cm}\) and the base is \(12\,\text{cm}\).

Answer

Base: \(12\,\text{cm}\) Height: \(7\,\text{cm}\)

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