Intermediate Geometry : How to find the length of the side of an equilateral triangle

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

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Example Question #1 : How To Find The Length Of The Side Of An Equilateral Triangle

The area of an equilateral triangle is , what is the length of each side?

Possible Answers:

Correct answer:

Explanation:

An equilateral triangle can be broken down into 2 30-60-90 right triangles (see image). The length of a side (the base) is 2x while the length of the height is . The area of a triangle can be calculated using the following equation:

Therefore, if  equals the length of a side:

A length of the side equals 2x:

 

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Example Question #1 : Equilateral Triangles

Asd

What is the area of this triangle if ?

Possible Answers:

Correct answer:

Explanation:

We know the formula for the area of an equilateral triangle is:

if  is the side of the triangle.

 

So, since we are told that , we can substitute in  for  and solve for the area of the triangle:

Example Question #3 : How To Find The Length Of The Side Of An Equilateral Triangle

Asd

Find  if the perimeter of this triangle is .

Possible Answers:

Correct answer:

Explanation:

This triangle is equilateral; we can tell because each of its sides are the same length, . To find the length of one side, we need to divide the perimeter by :

Example Question #2 : Equilateral Triangles

Asd

What is side  if the perimeter of this triangle is ?

Possible Answers:

Correct answer:

Explanation:

Since each of this triangle's sides is equal in length, it is equilateral. To find the length of one side of an equilateral triangle, we need to divide the perimeter by .

Example Question #5 : How To Find The Length Of The Side Of An Equilateral Triangle

Triangle

The height of the triangle is  feet.

What is the length of the base of the triangle to the nearest tenth?

Possible Answers:

Correct answer:

Explanation:

Since it is an equilateral triangle, the line that represents the height bisects it into a 30-60-90 triangle.

Here you may use  and solve for hypotenuse to find one of the sides of the triangle.

Use the definition of an equilateral triangle to know that the answer of the hypotenuse also applies to the base of the triangle.

Therefore,

Example Question #3 : Equilateral Triangles

The height of an equilateral triangle is 5. How long are its sides?

Possible Answers:

Correct answer:

Explanation:

The height of an equilateral triangle, shown by the dotted line, is also one of the legs of a right triangle:

Equilateral height

The hypotenuse is x, the length of each side in this equilateral triangle, and then the other leg is half of that, 0.5x. 

To solve for x, use Pythagorean Theorem:

square the terms on the left

combine like terms by subtracting 0.25 x squared from both sides

divide both sides by 0.75

take the square root of both sides

Example Question #4 : Equilateral Triangles

An equilateral triangle is placed on top of a square as shown by the figure below.

1

Find the perimeter of the shape.

Possible Answers:

Correct answer:

Explanation:

Recall that the perimeter is the sum of all the exterior sides of a shape. The sides that add up to the perimeter are highlighted in red.

13

Since the equilateral triangle shares a side with the square, each of the five sides that are outlined have the same length.

Recall that the height of an equilateral triangle splits the triangle into  congruent  triangles.

We can then use the height to find the length of the side of the triangle.

Recall that a  triangle has sides that are in ratios of . The smallest side in the given figure is the base, the second longest side is the height, and the longest side is the side of the triangle itself.

Thus, we can use the ratio and the length of the height to set up the following equation:

Plug in the given height to find the length of the side.

Now, since the perimeter of the shape consists of  of these sides, we can use the following equation to find the perimeter.

Example Question #8 : How To Find The Length Of The Side Of An Equilateral Triangle

An equilateral triangle is placed on top of a square as shown by the figure below.

2

Find the perimeter of the shape.

Possible Answers:

Correct answer:

Explanation:

Recall that the perimeter is the sum of all the exterior sides of a shape. The sides that add up to the perimeter are highlighted in red.

13

Since the equilateral triangle shares a side with the square, each of the five sides that are outlined have the same length.

Recall that the height of an equilateral triangle splits the triangle into  congruent  triangles.

We can then use the height to find the length of the side of the triangle.

Recall that a  triangle has sides that are in ratios of . The smallest side in the given figure is the base, the second longest side is the height, and the longest side is the side of the triangle itself.

Thus, we can use the ratio and the length of the height to set up the following equation:

Plug in the given height to find the length of the side.

Now, since the perimeter of the shape consists of  of these sides, we can use the following equation to find the perimeter.

Example Question #5 : Equilateral Triangles

An equilateral triangle is placed on top of a square, as shown by the figure below.

3

Find the perimeter of the shape.

Possible Answers:

Correct answer:

Explanation:

Recall that the perimeter is the sum of all the exterior sides of a shape. The sides that add up to the perimeter are highlighted in red.

13

Since the equilateral triangle shares a side with the square, each of the five sides that are outlined have the same length.

Recall that the height of an equilateral triangle splits the triangle into  congruent  triangles.

We can then use the height to find the length of the side of the triangle.

Recall that a  triangle has sides that are in ratios of . The smallest side in the given figure is the base, the second longest side is the height, and the longest side is the side of the triangle itself.

Thus, we can use the ratio and the length of the height to set up the following equation:

Plug in the given height to find the length of the side.

Now, since the perimeter of the shape consists of  of these sides, we can use the following equation to find the perimeter.

Example Question #6 : Equilateral Triangles

An equilateral triangle is placed on top of a square as shown by the figure below.

4

Find the perimeter of the shape.

Possible Answers:

Correct answer:

Explanation:

Recall that the perimeter is the sum of all the exterior sides of a shape. The sides that add up to the perimeter are highlighted in red.

13

Since the equilateral triangle shares a side with the square, each of the five sides that are outlined have the same length.

Recall that the height of an equilateral triangle splits the triangle into  congruent  triangles.

We can then use the height to find the length of the side of the triangle.

Recall that a  triangle has sides that are in ratios of . The smallest side in the given figure is the base, the second longest side is the height, and the longest side is the side of the triangle itself.

Thus, we can use the ratio and the length of the height to set up the following equation:

Plug in the given height to find the length of the side.

Now, since the perimeter of the shape consists of  of these sides, we can use the following equation to find the perimeter.

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