An angle in the coordinate plane is in standard position if its vertex is at the origin and one ray is on the positive x-axis. The ray on the x-axis is called the initial side. The other ray is the terminal side of the angle. The measure of an angle can be positive or negative.

• If the terminal side is rotated counterclockwise, then the measure of the angle is positive.
• If the terminal side is rotated clockwise, then the measure of the angle is negative.

Move the slider to see how the angle measure changes.