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Find the area of a triangle with base 13 inches and height 2 inches.

13 sq. in.

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Find the area of a triangle with base 14 inches and height 7 inches.

49 sq. in.

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The perimeter of a triangular garden is 24 feet. The lengths of two sides are 4 feet and 9 feet. How long is the third side?

Solution

Step 1. Read the problem. Draw the figure and label it with the given information. .
Step 2. Identify what you are looking for. length of the third side of a triangle
Step 3. Name. Choose a variable to represent it. Let c = the third side
Step 4. Translate.
Write the appropriate formula.
Substitute in the given information.

.
Step 5. Solve the equation. .
Step 6. Check:
.
Step 7. Answer the question. The third side is 11 feet long.
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The perimeter of a triangular garden is 24 feet. The lengths of two sides are 18 feet and 22 feet. How long is the third side?

8 ft

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The lengths of two sides of a triangular window are 7 feet and 5 feet. The perimeter is 18 feet. How long is the third side?

6 ft

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The area of a triangular church window is 90 square meters. The base of the window is 15 meters. What is the window’s height?

Solution

Step 1. Read the problem. Draw the figure and label it with the given information. .
Step 2. Identify what you are looking for. height of a triangle
Step 3. Name. Choose a variable to represent it. Let h = the height
Step 4. Translate.
Write the appropriate formula.
Substitute in the given information.

.
Step 5. Solve the equation. .
Step 6. Check:
.
Step 7. Answer the question. The height of the triangle is 12 meters.
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The area of a triangular painting is 126 square inches. The base is 18 inches. What is the height?

14 in.

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A triangular tent door has an area of 15 square feet. The height is 5 feet. What is the base?

6 ft

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Isosceles and equilateral triangles

Besides the right triangle, some other triangles have special names. A triangle with two sides of equal length is called an isosceles triangle    . A triangle that has three sides of equal length is called an equilateral triangle    . [link] shows both types of triangles.

Two triangles are shown. All three sides of the triangle on the left are labeled s. It is labeled “equilateral triangle”. Two sides of the triangle on the right are labeled s. It is labeled “isosceles triangle”.
In an isosceles triangle, two sides have the same length, and the third side is the base. In an equilateral triangle, all three sides have the same length.

Isosceles and equilateral triangles

An isosceles triangle has two sides the same length.

An equilateral triangle has three sides of equal length.

The perimeter of an equilateral triangle is 93 inches. Find the length of each side.

Solution

Step 1. Read the problem. Draw the figure and label it with the given information. .
Perimeter = 93 in.
Step 2. Identify what you are looking for. length of the sides of an equilateral triangle
Step 3. Name. Choose a variable to represent it. Let s = length of each side
Step 4. Translate.
Write the appropriate formula.
Substitute.

.
Step 5. Solve the equation. .
Step 6. Check:
.
.
Step 7. Answer the question. Each side is 31 inches.
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Find the length of each side of an equilateral triangle with perimeter 39 inches.

13 in.

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Find the length of each side of an equilateral triangle with perimeter 51 centimeters.

17 cm

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Arianna has 156 inches of beading to use as trim around a scarf. The scarf will be an isosceles triangle with a base of
60 inches. How long can she make the two equal sides?

Solution

Step 1. Read the problem. Draw the figure and label it with the given information. .
P = 156 in.
Step 2. Identify what you are looking for. the lengths of the two equal sides
Step 3. Name. Choose a variable to represent it. Let s = the length of each side
Step 4. Translate.
Write the appropriate formula.
Substitute in the given information.

.
Step 5. Solve the equation. .
Step 6. Check:
.
Step 7. Answer the question. Arianna can make each of the two equal sides 48 inches long.
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Practice Key Terms 6

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Source:  OpenStax, Prealgebra. OpenStax CNX. Jul 15, 2016 Download for free at http://legacy.cnx.org/content/col11756/1.9
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