# Circle Functions

This figure illustrates the geometry used to define the circle definitions of the trigonometric functions. Shown below are the definitions of the three main functions sine, cosine and tangent:

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There are six trigonometric functions that relate to the geometry of the right-triangle sine, cosine, tangent, cosecant, secant, and cotangent. The functions take the angle of a right triangle as input and return a ratio of two of its sides.

The sine function returns the sine of a number provided in radians. In geometric terms, the function returns the vertical component of the point formed by the angle on the unit circle.

The cosine function returns the cosine of an angle provided in radians. In geometric terms, the function returns the ratio of the right-triangle's adjacent side over its hypotenuse.

Given the angle of a right triangle as input returns the ratio of the triangle's opposite side over its adjacent side.