(PHP 4, PHP 5, PHP 7, PHP 8)
acos — Arc cosine
Returns the arc cosine of num in radians.
acos() is the inverse function of
cos() , which means that
$num == cos(acos($num)) for every value of
num that is in
the domain of acos().
numThe argument to process
The arc cosine of num in radians.
Parameter:
$num: A float value between -1 and 1. (Outside this range will return NAN)
Returns:
The arc cosine of the number in radians.
NAN (Not A Number) if the input is outside [-1, 1].
<?php
$cosValue = 0.5;
$angle = acos($cosValue); // returns angle in radians
echo $angle; // 1.0471975512 (which is ~60 degrees)
echo rad2deg($angle); // Convert to degrees: ~60
?>