ACOS(3)

NAME
       acos - arc cosine function

SYNOPSIS
       #include <<math.h>>

       double acos(double x);

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
       SVID 3, POSIX, BSD 4.3, ISO 9899

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