## When 2(a + b)(c + d)(a*c + b*d – x) is the square of an integer

The integers   $a, b, c, d$,   and   $x$   are such that

$a^2 \; + \; x \; = \; b^2$
$c^2 \; + \; x \; = \; d^2$

Show that   $2 \,(a + b) \,(c + d) \,(a \, c + b \, d - x)$   is the square of an integer