Hello!
There is no any example for acos() function. Please put this one below the acos() function's description.
Thank you!
Example:
<?php
$arg=0.5;
$val=acos($arg);
echo "acos(" . $arg . ") = " . $val . " radians.<br/>";
echo "Pi value = " . pi() . "<br/>";
echo "acos(" . $arg . ") = " . $val/pi()*180 . " degrees<br/>";
?>