# Intermediate Geometry : How to find the height of an equilateral triangle

## Example Questions

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

ΔABC is an equilateral triangle with side 12.

Find the height of ΔABC (to the nearest tenth).

10.6

10.2

10.0

10.4

9.8

10.4

Explanation:

Equilateral triangles have sides of all equal length and angles of 60°. To find the height, we can draw an altitude to one of the sides in order to split the triangle into two equal 30-60-90 triangles.

Now, the side of the original equilateral triangle (lets call it "a") is the hypotenuse of the 30-60-90 triangle. Because the 30-60-90 triange is a special triangle, we know that the sides are x, x, and 2x, respectively.

Thus, a = 2x and x = a/2.
Height of the equilateral triangle =

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

ΔABC is an equilateral triangle with side of length 8.

Find the height (to the nearest tenth).

7.5

7.3

7.1

6.7

6.9

6.9

Explanation:

Equilateral triangles have sides of equal length, with angles of 60°. To find the height, we can draw an altitude to one of the sides in order to split the triangle into two equal 30-60-90 triangles.

Now, the side of the original equilateral triangle (lets call it "a") is the hypotenuse of the 30-60-90 triangle. Because the 30-60-90 triange is a special triangle, we know that the sides are x, x, and 2x, respectively.

Thus, a = 2x and x = a/2.
Height of the equilateral triangle =

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

What is the height of an equilateral triangle with a side length of 8 in?

Explanation:

An equilateral triangle has three congruent sides, and is also an equiangular triangle with three congruent angles that each meansure 60 degrees.

To find the height we divide the triangle into two special 30 - 60 - 90 right triangles by drawing a line from one corner to the center of the opposite side. This segment will be the height, and will be opposite from one of the 60 degree angles and adjacent to a 30 degree angle. The special right triangle gives side ratios of , , and . The hypoteneuse, the side opposite the 90 degree angle, is the full length of one side of the triangle and is equal to . Using this information, we can find the lengths of each side fo the special triangle.

The side with length will be the height (opposite the 60 degree angle). The height is inches.

### Example Question #4 : How To Find The Height Of An Equilateral Triangle

What is the height of a triangle with side lengths 4, 4, 4?

Explanation:

To solve, it's easiest to first visualize the height's relationship with the rest of the triangle's sides:

The height is one of the legs of a right triangle. The hypotenuse is 4, and the other leg is 2, or half of the base side, 4. To determine the height, use Pythagorean Theorem:

subtract 4 from both sides

take the square root of both sides

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

If an equilateral triangle has a length of for all sides, what would be the heigh of the triangle? Round to the nearest tenth.

Explanation:

The following formula can be used to determine the height of an equilateral triangle when we are given the length of the sides:

### Example Question #6 : How To Find The Height Of An Equilateral Triangle

The equilateral triangle shown below has a side length of . Given this information, solve for the height of the triangle.

Explanation:

To solve for the height of an equilateral triangle, we can divide the triangle into two right triangles. In the below image, the bisecting line represents the height, and we can solve for height by applying the Pythagorean Theorem:

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

Find the height of an equilateral triangle with a side length of . Round your answer to the nearest tenth.