acos, acosf, acosl – arc cosine function

USAGE
       #include <math.h>

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

       Link with -lm.

DESCRIPTION
       The  acos()  function calculates the arc cosine of x; that is the value
       whose cosine is x.  If x falls outside the range -1 to 1, acos()  fails
       and errno is set.

RETURN VALUE
       The  acos() function returns the arc cosine in radians and the value is
       mathematically defined to be between 0 and PI (inclusive).

ERRORS
       EDOM   x is out of range.

CONFORMING TO
       SVr4, POSIX.1-2001, 4.3BSD, C89.  The float and  long  double  variants
       are C99 requirements.

SEE ALSO
       asin(3), atan(3), atan2(3), cacos(3), cos(3), sin(3), tan(3)