Question

Can ya'll help me factor this expression completely? x^2 -9

Answer 1

I assume you're supposed to factor it?

This is a special product, you might (hopefully :) remember from when you learned to FOIL/do binomial multiplication, that:

\(\Large (a-b)(a+b)=a^2-b^2\)

E.g., the product of a sum and a difference is = to the difference of the squares of the first and last terms.

So reverse that to factor: If you have a difference of squares, it factors into the product of the sum and the difference of the square roots:

\(\Large a^2-b^2=(a-b)(a+b)\)