## 1. Revision of the three basic trigonometric functions

The three basic trigonometric functions are defined for a right-angled triangle as ratios between pairs of sides as shown in the diagram.

You will notice that for the third angle of the triangle, which we can designate β:

β = 90 – α

sine β = cosine α

cosine β = sine α

tangent β = 1/tangent α

If you need to find further information on these functions, you should consult the helpsheet **Basic numerical skills: TRIANGLES AND TRIGONOMETRIC FUNCTIONS**.