Answer
$7(x^{2}+1)(x-1)(x+1)$
Work Step by Step
$ 7x^{4}-7\qquad$...factor out the GCF, $7$.
$=7(x^{4}-1)\qquad$...recognize the difference of two squares: $a^{2}-b^{2}=(a-b)(a+b)$
$=7(x^{2}-1)(x^{2}+1)\qquad$...once again, recognize the difference of two squares.
$=7(x^{2}+1)(x-1)(x+1)$
