Question

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

Answer 1

It is a FOIL product.

(9y² - 4x)(9y² + 4x)
9y²(9y² + 4x) - 4x(9y² + 4x)
9y²(9y²) + 9y²(4x) - 4x(9y²) - 4x(4x)
81y⁴ + 36xy² - 36xy² - 16x²
81y⁴ + 16x²