Calculate arccosine.
  Performs the trigonometric arc cosine operation on x and returns an angle in the range from 0 to PI expressed in radians.

Parameters.

x

Value between -1 and 1 whose arc cosine has to be calculated.

Return Value.
  Arc cosine of x.

Portability.
  Defined in ANSI-C.
  ANSI-C++ adds float and double overloaded versions of this function, with the same bahavior but being both, parameter and result, of one of these types.

Example.

/* acos example */
#include <stdio.h>
#include <math.h>

#define PI 3.14159265

main ()
{
  double param, result;
  param = 0.5;
  result = acos (param) * 180 / PI;
  printf ("Arccosine of %lf is %lf\n degrees", param, result );
  return 0;
}

See also.
  asin, atan, cos, sin, tan