[Adrian Schneider]

Yep! Personally I would pow(X, 2) to square it, but that doesn't matter. I gave it a trial run with 3, 4, and 5:

PHP Code:

<?php

$A = 3;
$B = 4;

if (isset($A) and isset($B) and !isset($C))
{
    $C = sqrt(pow($A, 2) + pow($B, 2));
}

echo $C;

?>

Both methods gave the desired result of 5.