atan2():

atan2(float $y,float $x);

<?Php
echo atan2(0,2); // Output is 0
echo "<br>";
echo atan2(1,3); // Output  0.32175055439664
echo "<br>";
echo atan2(-1,-3); // -2.8198420991932
echo "<br>";
echo atan2(4,2); // Output is 1.1071487177941
echo "<br>";
echo atan2(2,1); // Output is 1.1071487177941
echo "<br>";
echo atan2(90,180); // Output is 0.46364760900081
?>