Concept of an Angle

Two rays with a common starting point from an angle. One of the rays of an angle is called the initial side and the other is the terminal side. The angle is identified by showing the direction of rotation from the initial side to the terminal side.

An angle is said to be positive/negative if the rotation is anti-clockwise/clockwise. Angles are usually denoted by Greek letters such as \alpha (alpha), \beta (beta), \gamma (gamma), \theta (theta), etc.

In the figure below, \angle AOB is positive and \angle COD is negative.