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atan2 — Returns the arctangent based on an X-Y coordinate.


float atan2(x, y);
float x: X-axis value of point
float y: Y-axis value of point


Arctangent as a float


This function returns the value of the arctangent of the point denoted by the x and y parameters. The return value is in radians, in the range -pi to pi (approximately -3.14 to 3.14).


PHP 3 since 3.0.5, PHP 4

See also

See also acos() , asin() , atan() , cos() , sin() , tan()


Example 664. Calculate the arctangent of a coordinate

$tanx = -1;
$tany = 1;
echo "The arctangent of $tanx/$tany is ", atan2($tanx, $tany);

PHP Functions Essential Reference. Copyright © 2002 by New Riders Publishing (Authors: Zak Greant, Graeme Merrall, Torben Wilson, Brett Michlitsch). This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at The authors of this book have elected not to choose any options under the OPL. This online book was obtained from and is designed to provide information about the PHP programming language, focusing on PHP version 4.0.4 for the most part. The information is provided on an as-is basis, and no warranty or fitness is implied. All persons and entities shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from the information contained in this book.

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