====== Unit Circle ======
The Unit Circle is a circle of radius **1**. It is useful as certain angles have memorable coordinates that are helpful for solving trig problems by hand.

{{:math:unit-circle8_43216_lg.gif?600|}}

===== Using the Unit Circle for sin, cos, tan =====
  * $\sin \theta$ is equal to the y value of the coordinate
  * $\cos \theta$ is equal to the x value
  * $\tan \theta$ is equal to the y value **divided** by the x value((this uses the identity $\tan \theta = \frac{\sin \theta}{\cos \theta}$)).

Note that for $\tan \theta$, 90° and 270° ($\frac{\pi}{2}$ and $\frac{3\pi}{2}$ rad) are **undefined** as you cannot divide by zero((x values, or $\cos \theta$ is equal to zero in these two situations)). When calculating inverse trig functions, the solution is restricted between I and IV for $\sin$ and $\tan$, and I and II for $\cos$.