# Cosine Function (Cosine Ratio)

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In these lessons, we will learn the cosine function or cosine ratio and how to use the CAH formula.

The three common trigonometry functions are tangent, sine and cosine.
You may use want to use some mnemonics to help you remember the trigonometric functions. One common mnemonic is to remember the SOH-CAH-TOA.

In this lesson, we consider the cosine function.

The cosine of an angle is the ratio of the adjacent side and hypotenuse side.

Cosine is usually abbreviated as cos. Cosine θ can be written as cos θ.

Example:

Calculate the value of cos θ in the following triangle.

Solution:

### CAH Formula

Have a look at the following video for more examples on the cosine function:
This video illustrates how to use the Cosine formula (the CAH Formula) in high school and college trigonometry courses. The Cosine Ratio
An intro to the cosine ratio, some simple examples. Basic Trigonometry Formula - SOH-CAH-TOA
A basic introduction to defining the three major trigonometric functions (sine, cosine, tangent) are discussed using the mnemonic SOH-CAH-TOA.

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