Expert: Bobby Soltani - 8/2/2004

Question
factor the expression x^2-9

Answer
Hi Priscilla,

(x^2-9)

There are several properties you can use to help you factor expressions.  You can usually find them in your math book.  The one we will use here is:

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

For us, a = x and b = 3.  That is, (x^2-9) = (x^2-3^2)

So, using our formula above, we see that

(x^2-9) = (x+3)(x-3)

We can check our answer by using FOIL to multiply out the answer.  Let me know if you don't know how to use FOIL (First, Outer, Inner, Last).

Check:  (x+3)(x-3) = x^2+3x-3x-9 = x^-9

It works.

Let me know if you have any more questions.

Bobby