Acos () PHP Function

Definition: The acos () function is used in PHP to find the arccosine of a number. In acos (x) the value of x should be between -1 and 1, with -1 returning a value of PI. The acos() function returns the arccosine of a number as a numeric value value between 0 and PI radians.

Also Known As: Arccosine

Examples:

<?php
echo(acos(-0.5) . "<br />");
echo(acos(-1) . "<br />");
echo(acos(0) . "<br />");
echo(acos(1) . "<br />");
echo(acos(2))
?>

This will give you the results:
2.0943951023932
3.1415926535898
1.5707963267949
0
NAN