Answer
$9x^2y^4-16y^{2}$
Work Step by Step
The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$.
Hence here: $(3xy^2-4y)(3xy^2+4y)=(3xy^2)^2-(4y)^2=9x^2y^4-16y^{2}$
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