Answer type: function

variables {x}, {y},..
parameters: $a, $b, etc.

replacing variables
$varList = ['x', 'y'];#global
$valList = [[1,2], [3,2], [2,2]];#global

function evalFunc($a){
    global $message, $error_flag, $varList, $valList;
    $alist = [];
    for($i=0; $i<count($valList); $i++){
        for($j=0; $j<count($varList); $i++){
            $f = preg_replace('/\W'.$varList[$j].'\W/', $valList[$i][$j], $a);
            if($f!=$a){
                array_push($alist, eval($f) );
            }else{
                $message = "Error! Variable ".$varList[$j]." not found.";
                $error_flag = true;
                break 2;
            }
        }
    }
    return $alist;
}


students' input  1.23*x*sin(0.3*x)
regex for variables [^a-zA-Z]x[^a-zA-Z]    "\\W"+varname+"\\W"

preg_replace('//')

var forbiddenregex = /[^0-9A-Za-z\.\,\+\-\/\*\(\)\[\]\^\s]|alert|console|log|document|window|Element|form/;

preg_match()