# Missing Side of a Right Triangle Calculator

Table of contents

Missing side of a right triangleUsing the missing side of a right triangle calculatorOther related calculatorsFAQsThe missing side of a right triangle calculator will help you find the **third side or any third angle** for a right-angled triangle.

A triangle is right-angled if **one of the three angles is 90°**, i.e., any **two sides are perpendicular**. In this calculator, we use this property to deliver a calculator that enables you to find the missing side of a right triangle. Read on to understand how to find the missing side of a right triangle.

## Missing side of a right triangle

The formula that relates the sides of the triangle to its angles is the **sine law**. For a triangle having three sides as $a$, $b$, $c$, and the angles $\alpha$, $\beta$, and $\gamma$, it is given by the equation:

But we know that one of the angles is 90°. Therefore, the **sum of the other two angles is 90°**. Mathematically, if $\gamma = 90°$,

Using the above relation, we get:

The above relationship, along with the **Pythagoras theorem**, forms the core of this tool and is used to calculate the missing sides or angles for any right-angled triangle.

## Using the missing side of a right triangle calculator

Use the calculator to find the missing side of a right triangle having sides `9`

and `12`

.

- Enter the length of the
**first side**as`9`

. - Insert the length of the
**second side**as`12`

. - The calculator will return the
**third side**length as`15`

. - We can also get the
**angles**for the triangle as`36.87°`

and`53.13°`

using the missing side of a right triangle calculator.

### How do I find the missing side of a right triangle?

To find the missing side of a triangle:

**Divide**the length of the first side by the second side.- Find the
**inverse tangent**of the quotient to get the angle between the two sides. **Divide**the length of the first side by**sine**of the angle to obtain the third side of the triangle.

### What is the third side of a triangle having sides, 3 and 4?

The third side of the triangle is `5`

. First, we find the angle between the two sides, i.e., `arctan (3/4) = 36.87°`

. Then we divide the first side by the sine of angle obtained: `3/sin(36.87°) = 5`

.