# Really really basic factorization

• Jun 21st 2009, 04:04 AM
Peleus
Really really basic factorization
Hi all,

I feel pretty dumb posting this up, but here we go.

Factorise -
$9a^2 - 4b^2 + 12a + 8b$

I don't know why, I just never seem to be able to find the right combination for these.

I know we're meant to type out a common factor, I can't spot it though :(

I.e. for ax + bx + ay + by = a (x + y) + b (x + y) -> (a + b)(x + y)

Anyone want to point out the obvious combination for me?
• Jun 21st 2009, 04:16 AM
Quote:

Originally Posted by Peleus
Hi all,

I feel pretty dumb posting this up, but here we go.

Factorise -
$9a^2 - 4b^2 + 12a + 8b$

I don't know why, I just never seem to be able to find the right combination for these.

I know we're meant to type out a common factor, I can't spot it though :(

I.e. for ax + bx + ay + by = a (x + y) + b (x + y) -> (a + b)(x + y)

Anyone want to point out the obvious combination for me?

Erm , i think this will work .

$(9a^2-4b^2)+(12a+8b)$

$=(3a+2b)(3a-2b)+4(3a+2b)$

$
=(3a+2b)(3a-2b+4)
$
• Jun 21st 2009, 04:21 AM
Peleus
Thanks mate, I knew I was missing something. Just wasn't in the form I was expecting. I really need to stop expecting certain answers out of math questions and look at them objectively :)

Appreciate it.