# Measurement of angles

In this section, we will discuss about measurement of angles and measurement of sides.
Angle : When ray $\overrightarrow{OA}$ rotates about its end point 'O' and reach the position to OB then we say that $\angle$ AOB is formed.The OA is a initial side and OB is called terminal side of the angle. The end point 'O' about which the ray rotates is called the vertex of the angle.

Measure of an Angle: The measure of an angle is the amount of rotation from the initial side to the terminal side.
Sign of an angle: The sign of an angle is determined by the direction of rotation of the initial side into the terminal side. The angle may be positive or negative depends on the rotation of initial side clockwise or anticlockwise direction to get the terminal side.
Positive angle : When the initial side rotates to get the terminal side anticlockwise then the angle is positive angle.

Negative angle : When the initial side rotates to get the terminal side clockwise then the angle is negative angle.

Right angle : If the initial side rotates to terminal side after one quarter of a circle, then the angle formed is a right angle.