Definition:Angle

Definition
Given two intersecting lines or line segments, the amount of rotation about the intersection required to bring one into correspondence with the other is called the angle between them.

Measurement
Angles are usually measured in degrees, denoted by $$^\circ$$, or in radians, denoted by rad or without any unit. One full rotation is $$360^\circ$$ and $$2\pi$$ rad.

Types of Angle
Angles can be divided into categories:
 * Zero angle
 * Acute angles
 * Right angles
 * Obtuse angles
 * Straight angles
 * Reflex angles
 * Full angles

It is possible to have angles outside the $$[0^\circ ,360^\circ ]$$ or $$[0,2\pi ]$$ range, but it is usually preferable to convert these to angles inside this range by adding or subtracting multiples of $$360^\circ$$ or $$2\pi$$ rad.

Note
It is advisable to use radians, especially in calculus, since the derivatives of trigonometric functions work out without the necessity of multiplicative constants when angles are measured in radians (such as $$\frac{d}{dx}\sin x=\cos x$$).