Trigonometric ratios can be used in right-angled triangles.

Before you choose the most appropriate trig ratio, you must be able to label the sides of a right-angled triangle correctly in relation to the angle.

Look at the triangle above.

The side opposite the right-angle is called the HYPOTENUSE. It is the longest side.

The angle θº is shown.

The side opposite the angle θº is called the OPPOSITE side.

The side next to and touching the angle θº is called the ADJACENT side.