Question 695361
{{{x^4 -16}}}

{{{(x^2)^2-(4)^2}}}

using the identitity {{{a^2-b^2=(a+b)(a-b)}}}

we get

{{{(x^2+4)(x^2-4)}}}

using the same identity

{{{(x^2+4)(x+2)(x-2)}}}