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<!DOCTYPE html>
<html>
<body>
<?php
echo(atan2(0.50,0.50) . "<br>");
echo(atan2(-0.50,-0.50) . "<br>");
echo(atan2(5,5) . "<br>");
echo(atan2(10,20) . "<br>");
echo(atan2(-5,-5) . "<br>");
echo(atan2(-10,10));
?>
</body>
</html>
0.78539816339745
-2.3561944901923
0.78539816339745
0.46364760900081
-2.3561944901923
-0.78539816339745