# Cosine Function

## 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 |
---|---|---|

θ | angle | The 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