# Calculating an angle

The three trigonometric ratios can be used to calculate the size of an angle in a right-angled triangle.

### Example

Calculate the angle QPR. Give the answer to one decimal place.

Label the sides of the triangle , and .

Next choose the correct ratio from .

In the triangle the lengths and are known.

Use:

. Do not round this answer yet.

To calculate the angle use the inverse tan button on the calculator ( ).

Question

Calculate the angle KJL. Give the answer to one decimal place.

Label the sides of the triangle , and .

Next choose the correct ratio from .

In the triangle the lengths and are known.

Use:

. Do not round this answer yet.

To calculate the angle use the inverse cos button on the calculator ( ).