Now that we have spent some time understanding the basic features of the Unit Circle, we turn to the trigonometric functions and their relationship to the circle.

Fundamentally, we define the Cosine function as the horizontal component of the Unit Circle and the Sine function as the vertical component. The input to both of these functions is the terminal angle as we have previously defined.

This has some natural repercussions such as the relation \(\cos^2(\theta)+\sin^2(\theta)=1\)