## Algebra: A Combined Approach (4th Edition)

$4x^{2}-16y^{2}$
Using the product of sum and difference of two terms $(a+b)(a-b)=a^{2}-b^{2}$, $(2x-4y)(2x+4y)=(2x)^{2}-(4y)^{2}=4x^{2}-16y^{2}$.