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Mathematics LibreTexts

7: The Unit Circle: Sine and Cosine Functions

The trigonometric functions are functions of an angle. and relate the angles of a triangle to the lengths of its sides. They are important in the study of triangles and modeling periodic phenomena, among many other applications.

Thumbnail: The cosine function of an angle tt equals the x-value of the endpoint on the unit circle of an arc of length \(t\).