13-2 Angles and the Unit Circle

Objectives

To work with angles in standard position

To find coordinates of points on the unit circle

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An angle in the coordinate plane is in standard position when the vertex is at the origin and one ray is on the positive x-axis. The ray on the x-axis is the initial side of the angle. The other ray is the terminal side of the angle.

The measure of an angle in standard position is the amount of rotation from the initial side to the terminal side.

Essential Understanding The measure of an angle in standard position is the input for two important functions. The outputs are the coordinates (called cosine and sine) of the point on the terminal side of the angle that is 1 unit from the origin.

The measure of an angle is positive when the rotation from the initial side to the terminal side is in the counterclockwise direction. The measure is negative when the rotation is clockwise.

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