Hello, I am having trouble with this problem:

Find the product of (x+y-2) and (x+y+2)

Now, obviously I can use the, so to speak, "old fashion" way by foiling it. But they say in the solution that I can use a special product and rewrite it as:

[(x+y)-2][(x+y)+2]

And furthermore be written as:

(x+y)^2-2^2

Could someone please explain how they are doing this?

Thank you very much.