Question

(3z+3)(3z–3) How do I simplify this?

Answer 1

(3z+3)(3z–3)
9z^2-9z+9z-9
9z^2-9

Answer 2

What you have here is a case of "the difference between two squares."

Note that uri's 9z^2 - 9 is the difference of two squares: (3z)^2 - 3^2.

there is a formula for the "sum and difference of two squares":

\[a ^{2}-b ^{2}=(a-b)(a+b)\] Please compare this to the problem you've posted and ask yourself how you could applyl this formula to answering the question.