# Cosine

The cosine is the ratio of the length of an angle's adjacent side to the length of the hypotenuse in a right triangle.

Cosine is a high school-level concept that would be first encountered in a trigonometry course. It is listed in the California State Standards for Trigonometry.

### Prerequisites

Function: | A function is a relation that uniquely associates members of one set with members of another set. The term "function" is sometimes implicitly understood to mean continuous function, linear function, or function into the complex numbers. |

Right Triangle: | A right triangle is a triangle that has a right angle. The Pythagorean Theorem is a relationship among the sides of a right triangle. |

Trigonometry: | Trigonometry is the study of angles and of the angular relationships of planar and three-dimensional figures. |