factorise: 3x^2-6x-9=0.
I got the answer as (x-3)(x+9) but someone else got 3(x-3)(x+1), Which one is correct?

Question

factorise: 3x^2-6x-9=0. 
I got the answer as (x-3)(x+9) but someone else got 3(x-3)(x+1), Which one is correct?

will.h · Answer

what is the GCF here?

will.h · Answer

(Greatest common factor|)

agent0smith · Answer

You can pretty easily check your work here... expand this out, (x-3)(x+9), and do you get back the original?

will.h · Answer

3x^2 - 6x - 9
has a GCF of 3
divide each term by 3
3x^2/3 = x^2

-6x/3 = -2x

-9/3 = -3

so we now have 
3(x^2 - 2x - 3) now can we factor any further? 
yes! factoring by groups 
2 numbers when multiplied must equal to -2 and their sum is equal to -2 that would be 
1 and -3
3(x+1) (x-3 )

will.h · Answer

when multiplied must equal to -3 not -2 sorry

austin.l · Answer

I wish you could give out multiple medals. Agent's method is the quickest way to check and Will has the maths down.

Both are good methods for future reference.