Introduction to The Cosine Wave Function

Much like its sine counterpart, the cosine function, in terms of a triangle's vertices, expresses the ratio of the vertex adjacent to the angle we're taking the cosine of, over the hypotenuse.

What the hell does adjacent mean?
Adjacent essentially means "right next to it", sometimes "right next to it, touching it"

This function is written as To begin to connect these concepts together, you'll have to take a small refresher on a previous topic you've probably done before:

The Circle Equation