Chapter 5 - Section 5.3 - Special Products - Exercise Set - Page 367: 43

$x^{20}-25$

Using $(a+b)(a-b)=a^2-b^2$ or the special product of the sum and difference of like terms, the product of the given expression, $ (x^{10}+5)(x^{10}-5) ,$ is \begin{array}{l}\require{cancel} x^{10}(x^{10})-5(5) \\\\= x^{20}-25 .\end{array}