Let an angle whose measure in radians is be placed onto the Cartesian plane such that one of its rays corresponds to the nonnegative axis and one can go from the point to the point that is the intersection of the other ray of the angle with the circle by traveling exactly units on the circle. (If is positive, the distance should be traveled counterclockwise; otherwise, the distance should be traveled clockwise. Also, note that “other ray” is used quite loosely, as it may also correspond to the nonnegative axis also.) Then is the terminal ray of the angle.

The picture below shows the terminal ray of the angle .