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<!DOCTYPE html>
<html>
<body>
<?php
echo(atan(0.50) . "<br>");
echo(atan(-0.50) . "<br>");
echo(atan(5) . "<br>");
echo(atan(-5) . "<br>");
echo(atan(100) . "<br>");
echo(atan(-100));
?>
</body>
</html>
0.46364760900081
-0.46364760900081
1.373400766945
-1.373400766945
1.5607966601082
-1.5607966601082