# Thread: I need to know how to factor this

1. ## I need to know how to factor this

I don't know how to factor these four terms. I know factoring is all about finding factors but I need help to find out where that 3+x comes from and how can I do it.

2. Originally Posted by Alienis Back
I don't know how to factor these four terms. I know factoring is all about finding factors but I need help to find out where that 3+x comes from and how can I do it.
$\displaystyle x^3 + 3x^2 - 4x - 12 = x^2 (x+3) - 4(x+3)$.

And you know how to factorise by taking out a common factor ...?

3. Sure I know. I had tried factoring all terms by x+3 and resulted too complicated. Didn't know you could consider them sepatately. Thanks.

4. Originally Posted by Alienis Back
I don't know how to factor these four terms. I know factoring is all about finding factors but I need help to find out where that 3+x comes from and how can I do it.
$\displaystyle x^3 + 3x^2 - 4x - 12 = x^2 (x+3) - 4(x+3)$

take common (x + 3)

$\displaystyle =(x+3)(x^2-4)$

Now, can you proceed further???

5. Thanks guys. I did it!