In trigonometry, the **`cos ` function** of a right-angled triangle is defined as the length of the adjacent side over the longest side, i.e., the hypotenuse. An image of this is shown below:

The `cos` function in C++ works precisely like the cosine function in trigonometry. The return value of the `cos` function is the cosine of an angle given in radian.

To use the `cos` function, the `cmath` header file needs to be included in the program. This is done in the following way: 
```C++
#include <cmath>
```

# Parameters
The `cos` function takes one parameter in radians.

# Return value

The `cos` function returns the value between -1 and 1.

The function can have the return value of:
* float
* double
* long double

These types depend on the types of arguments the programmer gives to the functions. Below, Figure 2 shows the types of return types when different argument types are passed:



# Example

The code below shows how the `cos` function functions in C++:

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
  double x = 0.5;
  
  // result is in double
  cout << "cos(x) = " << cos(x) << endl;
  
  return 0;
}

How to use cos() in C++

To use the cos function in C++, include the cmath header; it returns cosine values between -1 and 1.