## College Algebra (6th Edition)

$(x^{2}+4)(x^{2}-4)$
If $a$ and $b$ are real numbers, we know that $a^{2}-b^{2}=(a+b)(a-b)$. In words, the difference of the squares of two terms factors as a product of a sum and a difference of those terms. Therefore, we know that $x^{4}-16=(x^{2}+4)(x^{2}-4)$. In this case, $a=x^{2}$ and $b=4$.