It outputs '56' to your console. That's all.

56.php

<?php
function math_fact($n) {
    $r = 1;
    for (; $n > 0; $n--) {
        $r *= $n;
    }
    return $r;
}

// 8!/(8-2)! == _8 P _2
$res = math_fact(8) / math_fact(8 - 2);
print $res;
?>