function
<cmath> <ctgmath>

# acos

double acos (double x);
double acos  (double x);
float acosf (float x);
long double acosl (long double x);
double acos (double x);
float acos (float x);
long double acos (long double x);
double acos (double x);
float acos (float x);
long double acos (long double x);
Compute arc cosine
Returns the principal value of the arc cosine of x, expressed in radians.

In trigonometrics, arc cosine is the inverse operation of cosine.

Header <tgmath.h> provides a type-generic macro version of this function.
This function is overloaded in <valarray> (see valarray acos).
Additional overloads are provided in this header (<cmath>) for the integral types: These overloads effectively cast x to a double before calculations (defined for T being any integral type).

This function is also overloaded in <complex> and <valarray> (see complex acos and valarray acos).

### Parameters

x
Value whose arc cosine is computed, in the interval [-1,+1].
If the argument is out of this interval, a domain error occurs.

### Return Value

Principal arc cosine of x, in the interval [0,pi] radians.
One radian is equivalent to 180/PI degrees.

If a domain error occurs, the global variable errno is set to EDOM.
If a domain error occurs:
- And math_errhandling has MATH_ERRNO set: the global variable errno is set to EDOM.
- And math_errhandling has MATH_ERREXCEPT set: FE_INVALID is raised.

### Example

 1234567891011121314 /* acos example */ #include /* printf */ #include /* acos */ #define PI 3.14159265 int main () { double param, result; param = 0.5; result = acos (param) * 180.0 / PI; printf ("The arc cosine of %f is %f degrees.\n", param, result); return 0; }

Output:
 The arc cosine of 0.500000 is 60.000000 degrees.