Radians

Radians are a measure of angular rotation, similar to degrees. 

Unlike degrees, radians are a real number, and do not have a unit.

An angle is said to be 1 radian if the length of the arc it makes on a circles circumference is equal to the radius of that circle.

Since the circumference of a circle is 2πr, there are 2π radians in a full rotation(360 degrees).

Because of this, radians are usually given in terms of π.

As well as the length of an arc, radians can be used to find the area of a sector or area of a segment of a circle.

Area of sector = θr^2                          2

where θ is the angle in radians, and r is the radius.

Area of sector= (θ - Sinθ)r^2                                2

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