# Factorising Cubic Equations - Maths Help

Found 2nd Mar 2009

I have a practise C1 exam tomorrow for my AS Level Maths & I am revising at the moment & cannot work out how to factorise a cubic equation which I have from a different past paper.

I could probably get it after a while but if anyone knows a way to generally factorise cubics I would be greatful if you could explain as my notes dont seem to make sence to me.

The said equation is x ^ 3 - 3x ^ 2 - 6x + 8

I have tried getting a linear & quadratic from it but I cant seem to get it right. In the end I need 3 linear factors of it.

If anyone could explain I would be very greatful. Its a non calculator paper so shouldnt be too complex.

Thanks alot

Cheers

James

I could probably get it after a while but if anyone knows a way to generally factorise cubics I would be greatful if you could explain as my notes dont seem to make sence to me.

The said equation is x ^ 3 - 3x ^ 2 - 6x + 8

I have tried getting a linear & quadratic from it but I cant seem to get it right. In the end I need 3 linear factors of it.

If anyone could explain I would be very greatful. Its a non calculator paper so shouldnt be too complex.

Thanks alot

Cheers

James

You'll need to guess a factor, such as 1 or -2 etc. It's a factor if the remainder is 0.

I learnt this at Higher level (A level) Maths, and it is very useful.

It was...

(x-1)(x^2 - 2x -8)

(x-1)(x+2)(x-4)

Need to go over them before tomorrow though haha!

Cheers for the replies!

At least you got it sorted.

May come in handy tomorrow.

Cheers

James

(x - 1)(x - 2)(x + 4)

(x - 1)(x + 2)(x - 4)

(x + 1)(x- 2)(x - 4)

(x - 1)(x - 1)(x +

(x - 1)(x + 1)(x +

The factor was just guessed. If if is non calculator, the factor will be a small number that you can do in your head. If the remainder is 0 (using synthetic division), then its a factor.