Question

Which expression is equivalent to (x + y)(x – y)?

Answer 1

x^2-y^2
you would get x^2+xy-xy+y^2
the xy and -xy cancel

Answer 2

We can't see any choices but it doesn't matter.  That's the factorization of the difference of two squares.  It's important to recognize either side when you see it; the usual next move is to replace it with the other side.

(x + y)(x – y) = x² - y²

Answer: x² - y²