# Factoring

• September 29th 2007, 01:01 PM
Factoring
I have to evaluate a limit, which I know how to do, but the problem I'm having is the factoring.

(x^3+2x^2-9x-18)/(x^2-9)

I know the denominator factors to (x+3)(x-3) but I can't do the numerator when there's 3 different levels of exponents for x.

Thanks

• September 29th 2007, 01:59 PM
red_dog
$x^3+2x^2-9x-18=x^3-3x^2+5x^2-15x+6x-18=$
$=x^2(x-3)+5x(x-3)+6(x-3)=(x-3)(x^2+5x+6)$
• September 29th 2007, 02:29 PM
ticbol
Quote:

I have to evaluate a limit, which I know how to do, but the problem I'm having is the factoring.

(x^3+2x^2-9x-18)/(x^2-9)

I know the denominator factors to (x+3)(x-3) but I can't do the numerator when there's 3 different levels of exponents for x.

Thanks

The numerator,
x^3 +2x^2 -9x -18

By just looking, you could see that (x+2) is in there.

= (x^3 +2x^2) -(9x +18)
= (x^2)(x+2) -9(x+2)
= (x+2)(x^2 -9)