The **`cos()`** function in D returns the cosine of a number. To be more specific, `cos()` returns the cosine of a number in radians. 

The mathematical representation of the `cos()` function is shown below.

>- `std.math` is required for this function.
>- The `cos()` function only works for right-angled triangles. 


# Syntax

---
```d
cos(number)
//number can be real, float, or double.
```
---

# Parameters

This function requires a number that represents an angle in radians as a parameter.

To convert degrees to radians, use the following formula:

---
```d
radians = degrees * ( PI / 180 )
```
---

# Return value

`cos()` returns the cosine of the number (in radians) that is sent as a parameter.

# Code
The following code shows how to use the `cos()` function in D.

import core.stdc.stdio;
import std.stdio;
//header required for function
import std.math;

int main()
{ 
    //positive number in radians
    writeln("The value of cos(2.3) ", cos(2.3));

    // negative number in radians
    writeln("The value of cos(-2.3) ", cos(-2.3));

    //converting the degrees angle into radians and then applying cos()
    // degrees = 180.0
    // PI = 3.14159265
    // result first converts degrees to radians then apply cos
    double result=cos(180.0 * (PI / 180.0));
    writeln("The value of cos(180.0 * (PI / 180.0)) ", result);
    return 0;
}

What is cos() in D?

Returns the cosine of a number in radians using std.math in D; accepts real, float, or double.