# Trig unit circle review

CCSS Math: HSF.TF.A.2

Review the unit circle definition of the trigonometric functions.

## What is the unit circle definition of the trigonometric functions?

The unit circle definition allows us to extend the domain of sine and cosine to

**all real numbers**. The process for determining the sine/cosine of any angle $\theta$ is as follows:- Starting from $(1,0)$, move along the unit circle until the angle that is formed between your position, the origin, and the positive $x$-axis is equal to $\theta$.
- $\sin(\theta)$ is equal to the $y$-coordinate of your point, and $\cos(\theta)$ is equal to the $x$-coordinate.

The other trigonometric functions can be evaluated using their relation with sine and cosine.

*Want to learn more about the unit circle definition? Check out this video.*

## Appendix: All trig ratios in the unit circle

Use the movable point to see how the lengths of the ratios change according to the angle.