Quadrants : On XY-plane let lines XOX' and YOY' are at right angles to each other.So these lines divides the XY -plane in four equal parts. Each part is known as Quadrant The lines XOX' and YOY' are known as X-axis and Y-axis respectively.These two lines taken together are known as coordinate axes.
Region of XOY ----> I QUADRANT
Region of YOX ----> II QUADRANT
Region of X'OY' ----> III QUADRANT
Region of YOX' ----> I QUADRANT

Angle in Standard position: An angle is said to be in standard position if its vertex coincides with the origin and the initial side coincides with positive direction of X-axis.

Angle in a quadrant : An angle is said to be in a particular quadrant, if the terminal side of the angle in standard position lies in that quadrant.

## Examples of quadrants and angles

Quadrant angle : An angle is said to be a quadrant angle, if the terminal side coincides with one of the axes.
Triangle of reference : If from any point P on the terminal side of an angle in standard position a perpendicular PM is drawn on x-axis, then the right angled triangle OMP, thus formed,is called the triangle of reference of the $\angle$XOP.

Co-terminal angle : Two angles with different measures but having the same initial sides and the same terminal sides are known as co-terminal angles.