Chapter 5 - Section 5.4 - Multiplying Polynomials - Exercise Set - Page 289: 35

$49a^2b^2-9c^2$

Using the special product of the sum and difference of like terms, $(a+b)(a-b)=a^2-b^2$, the given expression is equivalent to \begin{align*} & (7ab+3c)(7ab-3c) \\\\& (7ab)^2-(3c)^2 \\\\& 49a^2b^2-9c^2 .\end{align*}