# Unit Circle Notation

This figure illustrates the variables associated with the unit circle placed at the center of the cartesian and polar coordinate systems. The radius of the circle is of length . The point along the perimeter of the circle is labeled . The point is defined as , where the angle measured in radians. The point is also defined as by the and components.

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The unit circle is a circle of radius one placed at the origin of the coordinate system. This article discusses how the unit circle represents the output of the trigonometric functions for all real numbers.

The Cartesian Coordinate System describes space of one, two, and three dimensions. Each point in space is represented by its distance relative to the origin of the system.

The Polar Coordinate System describes points in space using an angle and radius relative to the origin.

Radians are a unit that measure angle using the radius of a circle. One radian is equal to the amount of rotation required to travel the length of one radius along the circumference of the circle.