# How to Find Inverse of cosine in Python

To find out the inverse of cosine in Python we use `math.acos()` function of Python Standard math Library. The inverse of cosine is also called arc cosine.

## `acos()` Function in Python

`math.acos()` function exists in Standard math Library of Python Programming Language. The purpose of this function is to calculate arc cosine or the inverse of the cosine of any given numeric value in the range of -1 and 1.

## Syntax of `acos()` Function in Python

The syntax of `acos()` function in Python is:
`math.acos( x )`

## Parameters of `acos()` Function in Python

`x` Any valid Python number (positive or negative within the range of -1 and 1). This parameter is required.
Note: if the `x` parameter is not a number, `acos()` function will return an error.

Python 2.x – Yes
Python 3.x – Yes

## Return Value of `acos()` Function in Python

`acos()` function returns a number ( a value of the inverse of cosine in radians).

## Python `acos()` Function Example

Output of Python `acos()` function:
`1.7721542475852274 1.5707963267948966 1.369438406004566`
Note that the unit of output number is radian.