The Probert Encyclopaedia of General Information

RADIAN

The radian is the SI unit (symbol rad) of plane angles, an alternative unit to the degree. It is the angle at the centre of a circle when the centre is joined to the two ends of an arc equal in length to the radius of the circle. There are 2 pi (approximately 6.284) radians in a full circle (360 degrees). One radian is approximately 57 degrees, and 1 degree is pi/180 or approximately 0.0175 radians. Radians are commonly used to specify angles in polar co-ordinates.
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