(PHP 4, PHP 5, PHP 7, PHP 8)
acos —Arc cosine
Returns the arc cosine ofnum in radians.acos() is the inverse function ofcos(), which means that$num == cos(acos($num)) for every value ofnum that is in the domain ofacos().
numThe argument to process
The arc cosine ofnum 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$angle;// 1.0471975512 (which is ~60 degrees)
echorad2deg($angle);// Convert to degrees: ~60
?>