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# C math acos() function

### C math acos() function

C math double acos(double x) function is used to return the arc cosine (inverse cosine) of any number x in radians. It takes a single argument x (1 ≥ x ≥ -1) and returns the arc cosine of it in radians. This function is included in <math.h> header file of C language.

Syntax:
`double acos(double x)`

### Parameters

x It is a floating point value in the interval [-1,+1].

Here is an example of acos() function:
``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main ()
{
double x, ret, val;
x = 0.75;
val = 180.0 / PI;
ret = acos(x) * val;
printf("The arc cosine of %lf is %lf degrees", x, ret);
return(0);
}
```
```
Output:
The arc cosine of 0.750000 is 41.409622 degrees
Example-2
``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main ()
{
double x, ret, val;
x = 0.555;
val = 180.0 / PI;
ret = acos(x) * val;
printf("The arc cosine of %lf is %lf degrees", x, ret);
return(0);
}
```
```
Output:
The arc cosine of 0.555000 is 56.289285 degrees