Positive and Negative Angles

Angle generated by a counter-clockwise rotation, we call angle a Positive Angle. 
On the other hand, if an angle is generated by a clockwise rotation we call angle a Negative Angle.

Positive Angle

An angle generated by anti-clockwise rotation is a positive angle. In figure let the initial side is OX. When this side is rotated by an angle θ in counter clockwise direction then angle is generated is called positive angle.

Negative Angle

An angle generated by clockwise rotation is a positive angle. In figure let the initial side is OX. When this side is rotated by an angle θ in clockwise direction then angle is called negative angle.

Is 30⁰ not same as -30⁰?

The answer to this question is NO. Here’s why? An angle has two attributes attached to it: Degree of rotation (or magnitude of rotation) and Direction of rotation (clockwise or anticlockwise). While these two angles have same degree of rotation, direction of rotation is just opposite as signified by there opposite signs. Therefore these two angles are different.

Summary

If an angle is generated by a counter-clockwise rotation, we call angle a positive angle.

On the other hand, if an angle is generated by a clockwise rotation we call angle a negative angle.