Cosine Function

Labeled Right Triangle

Summary

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

Input

Symbol(s)Name(s)Description
θangleThe angle of a right triangle.

Output

Returns the ratio of the right triangle’s adjacent side over its hypotenuse.

Explanation

The cosine function provides a mapping between the horizontal component of a right-triangle and the angle of the triangle. This can be visualized with the graph of cos(θ) from 0 to 2π below:

This can be geometrically visualized by putting a right-triangle and the graph side by side. Drag either of the points to interact with the graphic below:

Note, that the hypotenuse of the right triangle is one in the interactive above, but the function will return the same ratio for the input angle since what is returned is a ratio of the sides.

Good Links

Angle | concept
Radians | concept
Right Triangle | concept
Unit Circle | concept
Cosine | graph
Law of Cosines | concept
Sine | function
Trigonometric Functions | concept