Run »
<!DOCTYPE html> <html> <body> <?php echo(acos(0.64) . "<br>"); echo(acos(-0.4) . "<br>"); echo(acos(0) . "<br>"); echo(acos(-1) . "<br>"); echo(acos(1) . "<br>"); echo(acos(2)); ?> </body> </html>
0.87629806116834
1.9823131728624
1.5707963267949
3.1415926535898
0
NAN