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# C math cos() function

### C math cos() function

The C library function double cos(double x) is used to return the cosine of a radian angle x. It takes a single argument in radians and returns a value in type double in the range 1 to 1. This function is defined in <math.h> header file.

Syntax:
`double cos(double x);`

### Parameters:

x − It is the floating point value representing an angle expressed in radians.

Here is an example of cos() function:
``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main ()
{
double x, ret, val;
x = 60.0;
val = PI / 180.0;
ret = cos( x*val );
printf("The cosine of %lf is %lf degrees\n", x, ret);
return(0);
}
```
```
Output:
The cosine of 60.000000 is 0.500000 degrees
Example-2
``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main ()
{
double x, ret, val;
x = 90.0;
val = PI / 180.0;
ret = cos( x*val );
printf("The cosine of %lf is %lf degrees\n", x, ret);
return(0);
}
```
```
Output:
The cosine of 90.000000 is 0.000000 degrees