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),