PhoenixFire Group Title Factoring a cubic polynomial. $x^3-108x^2+3564x-34992$ I haven't needed to factor a cubic in a while and have forgotten how. Any help? I know the answers, just can't get them. one year ago one year ago

1. Kitt020912 Group Title

I know how to factor, but explaining it to someone is complicated. I haven't factored in so long either. I'll try to explain it. Sorry if I'm no help.. :/

3. Kitt020912 Group Title

Sorry I can't help you. >_< I'm a failed Amby on my first day. :c

4. drawar Group Title

$\begin{array}{l} {x^3} - 108{x^2} + 3564x - 34992 \\ = x({x^2} - 108x + 2916) + 648(x - 54) \\ = x{(x - 54)^2} + 648(x - 54) \\ = (x - 54)({x^2} - 54x + 648) \\ = (x - 54)(x - 36)(x - 18) \\ \end{array}$

5. Boblovesmath Group Title

@drawar from where did you 2916?

6. drawar Group Title

54^2

7. Boblovesmath Group Title

8. drawar Group Title

Yes but you have to bring it in, and subtract it later, that's the one and only trick when doing factorization of polynomials.

9. Boblovesmath Group Title

Where did you subtract it? And in which course did you take this?

10. drawar Group Title

3564=2916+648

11. drawar Group Title

I don't remember which course, I think it's common sense, no?

12. Boblovesmath Group Title

Can you please explain the before the last step? I don't get it, how did you reach to that point?

13. Boblovesmath Group Title

@drawar

14. drawar Group Title

Use a calculator to get 2 roots