Angles can be measured in either degrees or in radians. A complete revolution is defined as 360° (or 2symbol PI radians). Hence, a straight line forms an angle that is half the complete revolution, 180° or symbol PI radians. A right angle is one-fourth of a complete revolution, 90° or symbol PI/2 radians.

Related Terms: degree (°), point, radian, ray, side, vertex (in plane geometry)

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