PHP acos() Function – Inverse Cosine (Radians)

The acos() function in PHP returns the arccosine of a given argument, expressed in radians.

Signature: float acos(float $arg) Parameter $arg is the value whose inverse cosine is to be calculated.

Return value: the arccosine of $arg as a float in radians.

Example:

<?php
echo acos(0.64);
echo acos(0);
echo acos(-1);
echo acos(1);
echo acos(2);
?>

Corresponding output:

0.876298061168
1.57079632679
3.14159265359
0
-1.#IND