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.

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

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 ( ).