Chapter 5 - Exponents and Polynomials - 5.3 - Multiplying Polynomials - Problem Set 5.3 - Page 208: 86

$36x^2-1$

Using $(a-b)(a+b)=a^2-b^2$, or the product of the sum and difference of like terms, the given expression, $ (6x+1)(6x-1) ,$ is equivalent to \begin{array}{l}\require{cancel} (6x)^2-(1)^2 \\\\= 36x^2-1 .\end{array}