NUMBAT OER - Open Educational Resources

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.

Three basic trigonometric functions

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.