# The Unit Circle and the Cosine and Sine Functions

In this module we will introduce and study the two basic trigonometric functions – **Cosine **and **Sine**. As we will see any point in the x-y plane is some (radial) distance ** r** away from the origin on a line through the origin. Since a line through the origin is inclined at some angle

**the coordinates of**

*θ***and**

*x***of any point in the plane can be written in terms**

*y***and cosine and sine of the angle**

*r***.**

*θ***Review: **Pythagorean Theorem for right angle triangles, positive and negative angles, radian and de**g**ree measures.

**Learning Objectives:**

- Equation of a circle of radius
and center (0,0e).*r* - Equation of the Unit Circle
- Reference angle
- Definition of Cosine and Sine
- Domain and Range of the Cosine and Sine Functions