# Math Help - square difference

1. ## square difference

Factor this Equation:

x^2 + 6y - y^2 - 9

I figure, re-arrange.

x^2 - y^2 + 6y - 9

Group.

(x^2 - y^2) + (6y - 9)

Factor.

(x-y)(x+y) + 3(2y - 3)

Re-arrange.

3(2y-3) + (x-y)(x+y)

2. I wou have done
$\begin{array}{l}
x^2 - \left( {y^2 - 6y + 9} \right) \\
x^2 - \left( {y - 3} \right)^2 \\
\left( {x - y + 3} \right)\left( {x + y - 3} \right) \\
\end{array}
$

3. What about this one?

(x-1)^2 - 1

I know it's a^2 - b^2, but I can't lay it out.

Help please?

EDIT: Nevermind, got it.

4. $\left[ {\left( {x - 1} \right) - 1} \right]\left[ {\left( {x - 1} \right) + 1} \right]$ ??