atan2 man page on OpenDarwin

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```ATAN2(3)		 BSD Library Functions 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 computes the principal value of the arc tangent of
y/x, using the signs of both arguments to determine the quadrant of the
return value.

SPECIAL VALUES
atan2(�0, -0) returns �pi.

atan2(�0, +0) returns �0.

atan2(�0, x) returns �pi for x < 0.

atan2(�0, x) returns �0 for x > 0.

atan2(y, �0) returns -pi/2 for y > 0.

atan2(�y, -infinity) returns �pi for finite y > 0.

atan2(�y, +infinity) returns �0 for finite y > 0.

atan2(�infinity, +x) returns �pi/2 for finite x.

atan2(�infinity, -infinity) returns �3*pi/4.

atan2(�infinity, +infinity) returns �pi/4.

NOTES
The atan2() function is used mostly to convert from rectangular (x,y) to
polar (r,theta) coordinates that must satisfy x = r∗cos theta and y =
r∗sin theta.  In general, conversions to polar coordinates should be com‐
puted thus:

r	:= hypot(x,y);	... := sqrt(x∗x+y∗y)
theta     := atan2(y,x).

acos(3), asin(3), atan(3), cos(3), cosh(3), sin(3), sinh(3), tan(3),
tanh(3), math(3),

STANDARDS
The atan2() function conforms to ISO/IEC 9899:1999(E).

BSD			       November 18, 2002			   BSD
```
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