# How to Find Cos or Cosine in Python

Cosine is one of the basic trigonometric ratios. To find out cos or cosine in Python we use `math.cos()` function.

## `cos()` function in Python

`math.cos()` function is from Slandered math Library of Python Programming Language. The purpose of this function is to calculate cosine of any given number either the number is positive or negative.

## Syntax of `cos()`

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

## Parameters of `cos()` Function

`x` Any valid Python number (positive or negative). This parameter is required.
Note: if the `x` parameter is not a number, `cos()` function will return an `error`.

Python 2.x – Yes
Python 3.x – Yes

## Return Value of `cos()`

`cos()` function will return a floating point number (a value of cosine of `x` radian).

## Python `cos()` Function Example

``````# import math library
import math
print(math.cos(-0.2))
print(math.cos(0.0))
print(math.cos(0.2))
print(math.cos(1))
print(math.cos(5))``````

Output of Python `cos()` function:
```0.9800665778412416 1.0 0.9800665778412416 0.5403023058681398 0.28366218546322625```