# How to Use COS Function

The Cosine of an angle is the ratio of the length of the adjacent side to the length of the hypotenuse.

In excel, COS function returns the cosine of the given angle in radiant.

Formula:

= COS(number)

Explanations:

Number is required, the angle in radian that you want the cosine value.

Cautions:

The number (angle) needs to be in radians. When the angle is in degrees, using the angle multiply PI()/180 to convert the angle to radians first.