$_REQUEST[] is the correct variable that can retrieve values from both GET and POST methods. It's a superglobal array that contains data from $_GET, $_POST, and $_COOKIE. While $_GET and $_POST work for their specific methods, $_REQUEST combines them for convenience.
$_REQUEST[] is a superglobal array that aggregates data from $_GET, $_POST, and $_COOKIE, so it can retrieve a value regardless of whether it was sent via GET or POST. $_GET[] and $_POST[] only capture their respective single method, which is why they don't satisfy the 'either method' requirement here.