Radian/degree conversions; coterminal angles; complements and supplements

Understanding Coterminal Angles

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Coterminal Angles have the same terminal side. The terminal side is the side measured to. The initial side is the side measured from. For example, in this image 30 degrees, -330 degrees and 390 degrees all end on the same terminal side. They begin on the initial side. This means they are coterminal. -330 degrees is negative because it was measured counter clockwise.  30 degrees and 390 degrees are positive because they were measured clockwise. To find coterminal angles you add or subtract 2pi to or from the angle to find the radian measurement. To find the degree measurement 360 degrees must be added or subtracted. 2pi (or 360) is subtracted from positive angles and added to negative angles. Click Coterminal Angle Problems undeneath more to get some practice and sample problems!