# Thread: factoring trinomials by grouping

1. ## factoring trinomials by grouping

im having some trouble with these, heres an example of a problem...

3q^2+4q-4

sorry i have to ask on here, my math teacher is the worse math teacher in the world and never explains to us how to do anything, she just expects everyone to already know it. when we ask for help she says if you have to ask then you dont understand and if you dont understand you shouldnt be in her class.

thanks for the help

2. Originally Posted by formex
im having some trouble with these, heres an example of a problem...

3q^2+4q-4

sorry i have to ask on here, my math teacher is the worse math teacher in the world and never explains to us how to do anything, she just expects everyone to already know it. when we ask for help she says if you have to ask then you dont understand and if you dont understand you shouldnt be in her class.

thanks for the help
$\displaystyle 3q^2 + 6q - 2q - 4 = (3q^2 + 6q) - (2q + 4) = 3q{\color{red}(q + 2)} - 2{\color{red}(q + 2)} = {\color{red}(q + 2)} (3q - 2)$.

3. Originally Posted by mr fantastic
$\displaystyle 3q^2 + 6q - 2q - 4 = (3q^2 + 6q) - (2q + 4) = 3q{\color{red}(q + 2)} - 2{\color{red}(q + 2)} = {\color{red}(q + 2)} (3q - 2)$.
thanks a lot man.. the thing is though im having troubles understanding it, so do u mind if i ask u a few questions on how you got your answer?

ok, where did the 6q come from? also, how did 2 get a q beside it?

4. Originally Posted by formex
thanks a lot man.. the thing is though im having troubles understanding it, so do u mind if i ask u a few questions on how you got your answer?

ok, where did the 6q come from? also, how did 2 get a q beside it?
Read this: Algebra Help - Factoring a Quadratic Trinomial by Grouping

5. ahh, excellent man, awesome link, thanks!

6. there wouldn't happen to be a formula to finding out the common monomial would there?

for example, if the problem was like this

9v^2 + 5v - 4
(9)(-4)=-36

i'd then need a set of integers that's sum is 5 and product is -36, which is sometimes difficult to find. is there a formula you can use to get the common integers? thanks again

7. Originally Posted by formex
there wouldn't happen to be a formula to finding out the common monomial would there?

for example, if the problem was like this

9v^2 + 5v - 4
(9)(-4)=-36

i'd then need a set of integers that's sum is 5 and product is -36, which is sometimes difficult to find. is there a formula you can use to get the common integers? thanks again
There isn't really a shortcut - it just comes with practice. 3v * 3v will not work with -2*2 because it will be the difference of two squares.
As 5 > 0 it follows that the minus sign will go next to the 9v giving

(9v-4)(v+1)