Trigonometry

Trigonometry is the study of triangles. Three trigonometric functions that are specific to right-angled triangles are sine, cosine and tangent, often shortened to sin, cos and tan.

 

Firstly it is important to understand the terms used to describe the three sides of a right triangle:
Hypotenuse – The side opposite the right angle, always the longest side
Opposite – The side opposite the angle you’re working with
Adjacent – The side next to the angle you’re working with

Sin = Opposite / Hypotenuse

Cos = Adjacent / Hypotenuse

Tan = Opposite / Adjacent

The acronym SOHCAHTOA is helpful to remember which sides go which each function.

 

These functions can be used to relate the angles in the triangle to the side lengths.