## Precalculus (6th Edition) Blitzer

$49x^2-9y^2$
RECALL: $(a+b)(a-b) = a^2-b^2$ Multiply the given expression using the formula above with $a=7x$ and $b=3y$ to obtain: $=(7x)^2-(3y)^2 \\=49x^2-9y^2$