The **`numpy.cos()` method** in Python calculates the ratio of the length of the side nearest to the angle to the length of the hypotenuse. This function returns the cosine of a number. To be more precise, it returns the cosine of a _radian_. 

A visual representation of the cosine ($cos$) is as follows.



#   
## Syntax
```
numpy.cos(x, out=None)
```
## Input parameters
- **`x`**: This method takes an array of _radian_ numbers as an input.
- **`out=None`**: This is an optional parameter in the `numpy.cos()` function. This could be `ndarray`, `None`, or `tuple` of the `ndarray`. This parameter identifies a location where the solution or output is stored.

## Returns
This method returns an `ndarray` containing the cosine values of radian numbers from the input. The output may be scalar if the input is scalar.

## Example

import numpy as np
# Creating an array
array = np.array([0, np.pi/2, np.pi])

#Calculating the cosine of the values
result = np.cos(array)

#Using the out parameter
new_result = np.array([0, np.pi/2, np.pi])
np.cos(array, out = new_result)

print("Cosine of values : ", result)
print("New Result array : ", new_result)

## Explanation
- Line 3: We create an array using the `np.array()` method.
- Line 6: We calculate the cosine of the values in the `array`.
- Line 9: We create a new array in this statement.
- Line 10: We calculate the cosine values and store them in the `new_result` array using the `out` parameter. 

> **Note**: Providing the `out` parameter in the `numpy.cos()` function will store the result in the `out` parameter, and return a reference to it.

What is numpy.cos() in Python?

numpy.cos() function calculates cosines of radians, returns ndarray of cos values, supports optional output.