# 1.6: Relationships of Sides in 30-60-90 Right Triangles

**At Grade**Created by: CK-12

**Practice**Relationships of Sides in 30-60-90 Right Triangles

You are working on a project in your Industrial Arts class. You have been instructed to design a building. You have a plastic triangular piece that helps you with straight edges and designs. This triangle has interior angles of

You trace out the bottom and left edge of the triangle on the paper to serve as the side and bottom of the structure. Looking at the length of the base of the building, you see that it is 7 inches long. Can you determine what the height of the building is from this information?

### 30-60-90 Right Triangles

To understand the ratios of the sides, start with an equilateral triangle with an altitude drawn from one vertex.

Recall from geometry that an altitude,

From this we can conclude that the length of the longer leg is the length of the short leg multiplied by

Notice, that the shortest side is *always* opposite the smallest angle and the longest side is *always* opposite

#### Finding the Length of Missing Sides

1. Find the lengths of the two missing sides in the

Determine which side in the

2. Find the lengths of the two missing sides in the

Determine which side in the

17 is the hypotenuse because it is opposite the right angle. In the

3. Find the lengths of the two missing sides in the

Determine which side in the

15 is the long leg because it is opposite the

Multiplying

### Examples

#### Example 1

Earlier, you were asked to design a building.

Since you know the ratios of sides of a 30-60-90 triangle, you know that since the bottom side has a length of

#### Example 2

Find the lengths of the two missing sides in the

Since the given side has a length of 8 and is the side which is opposite the right angle, we know that this is the "2x" side of the triangle. Therefore, the short side of the triangle is

#### Example 3

Find the lengths of the two missing sides in the 30-60-90 triangle below.

We can see that the shortest side of the triangle has a length of 3 while the longest side has a length of 6 and the other side has a length of

#### Example 4

Find the angles in the

The length of the given side is \begin{align*}3\sqrt{3}\end{align*}, and is opposite the \begin{align*}60^\circ\end{align*} angle. This means that the side opposite the \begin{align*}30^\circ\end{align*} angle is \begin{align*}3\end{align*}, and the length of the side opposite the \begin{align*}90^\circ\end{align*} angle is \begin{align*}6\end{align*}

### Review

- In a 30-60-90 triangle, if the shorter leg is 8, then the longer leg is __________ and the hypotenuse is ___________.
- In a 30-60-90 triangle, if the shorter leg is 12, then the longer leg is __________ and the hypotenuse is ___________.
- In a 30-60-90 triangle, if the longer leg is 10, then the shorter leg is __________ and the hypotenuse is ___________.
- In a 30-60-90 triangle, if the shorter leg is 16, then the longer leg is __________ and the hypotenuse is ___________.
- In a 30-60-90 triangle, if the longer leg is 3, then the shorter leg is __________ and the hypotenuse is ___________.
- In a 30-60-90 triangle, if the shorter leg is \begin{align*}x\end{align*}, then the longer leg is __________ and the hypotenuse is ___________.
- In a 30-60-90 triangle, if the longer leg is \begin{align*}x\end{align*}, then the shorter leg is __________ and the hypotenuse is ___________.
- A rectangle has sides of length 7 and \begin{align*}7 \sqrt{3}\end{align*}. What is the length of the diagonal?
- Two (opposite) sides of a rectangle are 15 and the diagonal is 30. What is the length of the other two sides?
- What is the height of an equilateral triangle with sides of length 6 in?
- What is the area of an equilateral triangle with sides of length 10 ft?
- A regular hexagon has sides of length 3 in. What is the area of the hexagon?
- The area of an equilateral triangle is \begin{align*}36 \sqrt{3}\end{align*}. What is the length of a side?
- If a road has a grade of \begin{align*}30^\circ\end{align*}, this means that its angle of elevation is \begin{align*}30^\circ\end{align*}. If you travel 3 miles on this road, how much elevation have you gained in feet (5280 ft = 1 mile)?
- If a road has a grade of \begin{align*}30^\circ\end{align*}, this means that its angle of elevation is \begin{align*}30^\circ\end{align*}. If you travel x miles on this road, how much elevation have you gained in feet (5280 ft = 1 mile)?

### Review (Answers)

To see the Review answers, open this PDF file and look for section 1.6.

### Notes/Highlights Having trouble? Report an issue.

Color | Highlighted Text | Notes | |
---|---|---|---|

Please Sign In to create your own Highlights / Notes | |||

Show More |

### Image Attributions

Here you'll learn what a 30-60-90 triangle is, the relationship between the lengths of the sides, and how to find the length of an unknown side.

**Save or share your relevant files like activites, homework and worksheet.**

To add resources, you must be the owner of the Modality. Click Customize to make your own copy.