In a unit circle, where is the angle desired, and can be defined as and . Using the function of the unit circle, , another equation for the unit circle is found, . When working with trigonometric functions, it is mainly useful to use angles with measures between 0 and radians, or 0 through 90 degrees. It is possible to have higher angles than that, however. Using the unit circle, two identities can be found: and for any integer.
The unit circle can substitute variables for trigonometric functions.