In a unit circle, where formula_2 is the angle desired, formula_3 and formula_4 can be defined as formula_5 and formula_6. Using the function of the unit circle, formula_1, another equation for the unit circle is found, formula_8. When working with trigonometric functions, it is mainly useful to use angles with measures between 0 and formula_9 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: formula_10 and formula_11 for any integer formula_12.