Question

How do you multiply `(x^2 + 2y) (x^2 - 2y)`?

Answer 1

This is a sum multiplied a difference. The rule is:

`(a+b)(a-b)=a^2-b^2`, so:

`(x^2 + 2y) (x^2 - 2y)=(x^2)^2-(2y)^2=x^4-4y^2`.