# Thread: factorising cubics

1. ## factorising cubics

Can someone please explain to me the steps slowly how to factorise cubics??

The question is Factorise (s^2 - 3s + 2)(s+4)
And the answer is (s-1)(s-2)(s-4)

I just don't get how they got from the first step to the last step.. Here's what I tried to do...

s^3 + 4s^2 -3s^2 -12s + 2s +8
s^3 + s^2 -10s + 8
s(s^2 + s - 10) + 8
And this is where i don't know what to do next ><

2. Originally Posted by gconfused

The question is Factorise (s^2 - 3s + 2)(s+4)
The answer to this question is not

Originally Posted by gconfused
And the answer is (s-1)(s-2)(s-4)

The answer is (s-1)(s-2)(s+4)

This is because $s^2 - 3s + 2 = (s-1)(s-2)$

3. omigosh im so stupid ><.
yeahh you're right, that is the answer haha i get it now

4. Happy to help my fellow Aussie!

5. One thing I keep telling students: If you have a problem that is already (partially) factored don't multiply it! Factoring is typically much harder than multiplying. If it is already factored for you, use that!