## Introductory Algebra for College Students (7th Edition)

$a^2b^2-1$
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, $(ab+1)(ab-1) ,$ is \begin{array}{l}\require{cancel} (ab)^2-(1)^2 \\\\= a^2b^2-1 .\end{array}