Answer
$\color{blue}{(x^2+4)(x+2)(x-2)}$
Work Step by Step
With $16=4^2$ and $x^4=(x^2)^2$, the given expression is equivalent to:
$=(x^2)^2-4^2$
RECALL:
$a^2-b^2=(a+b)(a-b)$
Factor the expressions using the formula above with $a=x^2$ and $b=4$ to obtain:
$=(x^2+4)(x^2-4)
\\=(x^2+4)(x^2-2^2)$
Factor the second binomial using the same formula to obtain:
$=\color{blue}{(x^2+4)(x+2)(x-2)}$
