(a+b)^2 – (a-b)^2
Since both are squares you end up with
(a+b +a-b) * (a+b –(a-b))
First set of parenthesis add the 2 a’s together to get 2a and subtract b from b
So you end you with 2a
Now you have
2a(a+b –(a-b))
Second set of parenthesis you subtract a from a and then have b+b left which equals 2b
So now you have 2a times 2b
Which equals 4ab