Unit circle
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 .