redhat man page for atan2

ATAN2(3)						     Linux Programmer's Manual							  ATAN2(3)

NAME
       atan2 - arc tangent function of two variables

SYNOPSIS
       #include <math.h>

       double atan2(double y, double x);

DESCRIPTION
       The  atan2()  function  calculates  the	arc  tangent of the two variables x and y.  It is similar to calculating the arc tangent of y / x,
       except that the signs of both arguments are used to determine the quadrant of the result.

RETURN VALUE
       The atan2() function returns the result in radians, which is between -PI and PI (inclusive).

CONFORMING TO
       SVID 3, POSIX, BSD 4.3, ISO 9899

SEE ALSO
       acos(3), asin(3), atan(3), cos(3), sin(3), tan(3)

								    1993-06-08								  ATAN2(3)