redhat man page for atan

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

NAME
       atan - arc tangent function

SYNOPSIS
       #include <math.h>

       double atan(double x);

DESCRIPTION
       The atan() function calculates the arc tangent of x; that is the value whose tangent is x.

RETURN VALUE
       The atan() function returns the arc tangent in radians and the value is mathematically defined to be between -PI/2 and PI/2 (inclusive).

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

SEE ALSO
       acos(3), asin(3), atan2(3), cos(3), sin(3), tan(3)

								    1993-06-08								   ATAN(3)