Question

What’s [(x-y) + 7] times [(x-y) - 7]?

Answer 1

Explanation:

Let z = x - y

The given expression translates into

(z + 7)(z - 7) which is going to give you the difference of squares.

z^2 - 49

Now you need to know what z^2 is

z = x -y

z^2 = x^2 - 2xy + y^2

So the answer becomes

x^2 - 2xy + y^2 - 49