Chapter 5 - Mid-Chapter Check Point - Page 378: 9

$x^4-4$

Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the product of the given expression, $ (x^2+2)(x^2-2) ,$ is \begin{array}{l}\require{cancel} (x^2)^2-(2)^2 \\\\= x^4-4 .\end{array}