# Trigonometric Ratio: Cosine

How to solve cosine (trigonometric ratio) problems: definition, examples, and their solutions.

## Definition

Cosine is the ratio of a right triangle's

(Adjacent side) / (Hypotenuse).**CAH**:**C**osine = (**A**djacent) / (**H**ypotenuse)

## Example 1

Cosine: **CAH**.

So **c**os *A* = (**A**djacent side, 4) / (**H**ypotenuse, 5).

## Example 2

Cosine: **CAH**.

So **c**os *A* = (**A**djacent side, 5) / (**H**ypotenuse, 13).

## Example 3

Cosine: **CAH**.

So **c**os *A* = (**A**djacent side, 6) / (**H**ypotenuse, *x*) = 3/5.