The three trigonometric ratios; sine, cosine and tangent are used to calculate angles and lengths in right-angled triangles. The sine and cosine rules calculate lengths and angles in any triangle.

Part of

The cosine rule is:

This version is used to calculate lengths.

It can be rearranged to:

This version is used to calculate angles.

Calculate the length BC. Give the answer to three significant figures.

Use the form to calculate the length.

. Do not round this answer yet.

BC = 4.86 cm

- Question
Calculate the angle QPR. Give the answer to three significant figures.

Use the form to calculate the angle.

. Do not round this answer yet.

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

= 33.6°