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 radiansecho $angle; // 1.0471975512 (which is ~60 degrees)echo rad2deg($angle); // Convert to degrees: ~60?>