In this tutorial, you will learn about C math library function cos() that computes the cosine.

`cos()` is the standard C math library function that is defined in math library `math.h`.

``#include<math.h>``

## Function prototype of C math library function cos()

``double cos( double x );``

where,

x = angle in radians ( floating point value )

### Return Value of cos( )

This function returns the cosine value of `x` that ranges in the interval [ -1, 1 ].

The return type is double.

## Example: C program to demonstrate the use of math library function cos()

``````/*Use of math library function cos()*/

#include<stdio.h>
#include<math.h>

#define PI 3.1415926

int main()
{
double x ;

x = 60;
//calculation of cosine
printf("\ncos( %.2lf ) = %.2lf \n", x, cos( (x * PI) / 180 ));

x = 180;
//calculation of cosine
printf("\ncos( %.2lf ) = %.2lf \n", x, cos( (x * PI) / 180 ));

return 0;
}
``````

Output

Explanation

In the above program, we have calculated the cosine of `x`.

We have defined macro `PI` for representing the value of `pi`.
The input of cos( ) can be any value.