# C acos()

The acos() function defined in the math.h header file. It helps to return the arc cosine value of the given number in radians. The arc cosine means inverse cosine value.

``````
double acos(double x); #where x can be in int, float or long double
```
```

Also, two functions acosf() and acosl() were used with type float and long double respectively.

``````
float acosf(float x);
long double acosl(long double x);
```
```

## acos() Parameters:

The acos() function takes a single parameter between the range 1 ≥ x ≥ -1. Using cast operator we can explicitly convert the type to double to find the arc cosine of type int, float, or long double.

Parameter Description Required / Optional
double value A double value between - 1 and +1 Required

## acos() Return Value

The return value of acos() function is in the range of [0.0, π] in radians.

Input Return Value
x = [-1, +1] [0, π] in radians
-1 > x or x > 1 NaN (not a number)

## Examples of acos()

### Example 1: Working of acos() function in C?

``````
#include <stdio.h>
#include <math.h>
int main()
{

const double PI =  3.1415926;
double v, output;

v =  -0.5;
output = acos(v);
printf("The Inverse of cos(%.2f) = %.2lf in radians\n", v, output);

output = acos(v)*180/PI;
printf("The Inverse of cos(%.2f) = %.2lf in degrees\n", v, output);

// paramter not in range
v = 1.2;
output = acos(v);
printf("The Inverse of cos(%.2f) = %.2lf", v, output);

return 0;
}
```
```

Output:

```
The Inverse of cos(-0.50) = 2.09 in radians
The Inverse of cos(-0.50) = 120.00 in degrees
The Inverse of cos(1.20) = nan
```

### Example 2: How acosf() and acosl() functions worked in C?

``````
#include <stdio.h>
#include <math.h>
int main()
{
float f, fcosx;
long double l, lcosx;

// type float
f = -0.505405;
fcosx = acosf(f);

//type long double
l = -0.50540593;
lcosx = acosl(l);

printf("acosf(x) is equal to %f in radians\n", fcosx);
printf("acosl(x) is equal to %Lf in radians", lcosx);

return 0;
}
```
```

Output:

```
acosf(x) is equal to 2.100648 in radians
acosl(x) is equal to 2.100649 in radians
```
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