# Thread: [SOLVED] Expand and Simplify

1. ## [SOLVED] Expand and Simplify

5(1 - xy)(1 + xy)

2. Originally Posted by coolman21
5(1 - xy)(1 + xy)
You should know the difference of two squares factorisation: $a^2-b^2=(a-b)(a+b)$, then recognise that is what you need with $a=1$ and $b=xy$ to get:

$
5(1 - xy)(1 + xy) =5(1-x^2y^2)
$

RonL

3. ## Expand and simplify

Originally Posted by coolman21
5(1 - xy)(1 + xy)
expanding
$5(1 - xy)(1 + xy)$
$(5-5xy)(1 + xy)$
$5*1+5*xy-5xy*1-(5xy)(xy)$
$5+5xy-5xy-5x^2y^2$

simplifying
$5-5x^2y^2$
$5-5(xy)^2$
$5(1-(xy)^2)$

But if you know the formula mentioned in the other post, you can save yourself some of this trouble.

I am showing all the steps here (just in case) since the problem said "expand and simplify"