Question

Which is equivalent to (9y2 – 4x)(9y2 + 4x), and what type of special product is it?

Answer 1

Consider the expression $(9y^2- 4x)(9y^2 + 4x) .$ You can see that in both brackets are the same terms $9y^2$ and $4x$, but signs are different. So you can use formula for the difference of squares:

$a^2-b^2=(a-b)(a+b).$

According to this formula,

$(9y^2-4x)(9y^2+4x)=(9y^2)^2-(4x)^2=9^2\cdot (y^2)^2-4^2\cdot x^2=81y^4-16x^2.$

Answer: correct choice is B.

Answer 2

I believe the answer is the second choice.
81y^4 - 16x^2, the difference of squares.