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<!DOCTYPE html> <html> <body> <?php echo(asin(0.64) . "<br>"); echo(asin(-0.4) . "<br>"); echo(asin(0) . "<br>"); echo(asin(-1) . "<br>"); echo(asin(1) . "<br>"); echo(asin(2)); ?> </body> </html>
0.69449826562656
-0.41151684606749
0
-1.5707963267949
1.5707963267949
NAN