Negative Values

Figure 12.15 involves negative values on the x axis. The negative values reflect the fact that angles can be negative. When an angle is negative, the direction you move on the perimeter of the circle is in a counterclockwise direction. In this situation, you measure angles and radians just as you would if you moved in a clockwise direction, except that the value of − (−90°) is found on the lower part of the y axis, while − (−180°) is found on the upper part. Figure 12.16 illustrates a few negative angles you encounter as you move along a negative arc of a unit circle.