php man page for atan2

ATAN2(3)								 1								  ATAN2(3)

atan2 - Arc tangent of two variables

SYNOPSIS
       float atan2 (float  $y, float  $x)

DESCRIPTION
	This  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.

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

PARAMETERS
	      o $y
		- Dividend parameter

	      o $x
		- Divisor parameter

RETURN VALUES
	The arc tangent of $y/$x in radians.

SEE ALSO
       atan(3).

PHP Documentation Group 														  ATAN2(3)