# Chapter 5: Trigonometric Functions of Angles

In the previous chapters we have explored a variety of functions which could be combined to form a variety of shapes. In this discussion, one common shape has been missing: the circle. We already know certain things about the circle, like how to find area and circumference, and the relationship between radius and diameter, but now, in this chapter, we explore the circle and its unique features that lead us into the rich world of trigonometry.

### Contributors

- David Lippman (Pierce College)
- Melonie Rasmussen (Pierce College)