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