The radian is a measure unit of angle used in the higher mathematics. The magnitude of an angle is one radian, if the arc corresponding the angle as a central angle of a circle is equally long as the radius of the circle. Thus, a radian is equal to degrees. It is in degrees, minutes and seconds approximately

In degrees, a circle has 360 degrees, while in radians a circle has radians. In fact, many angles of equilateral polygons are equal to a multiple of divided by some integer: for example, the interior angle of an equilateral triangle's vertex is , while the interior angle of an equilateral pentagon's vertex is .