A radian is an angular measurement.

If we draw two straight lines that cross at the centre of a circle such that the length of the circumference between them (an arc) equals the radius, then the angle between these lines is 1 radian.

The angular circumference of a circle is 2π radians, or 360 degrees, so that:

- 1 radian = 360/2π degrees = 57
^{o}17’ 44.8”.

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