# factoring trinomials?

• Apr 17th 2008, 08:10 PM
helpmee
factoring trinomials?
4n^2-36??
• Apr 17th 2008, 08:18 PM
Jen
Factor out a 4 and use the difference of squares.

Give it a try. It is similar to the earlier ones we did.
• Apr 17th 2008, 08:20 PM
helpmee
so n^2-8?
i dont know what to do after that...
• Apr 17th 2008, 08:21 PM
Jen
so your solution should look like $4(n+c)(n-c)$ Where c is some constant. Remember that you should be able to multiply it all back out and it should look like the original.
• Apr 17th 2008, 08:22 PM
o_O
$4n^{2} - 36 = 4\left(n^{2} - 9\right)$

Since $36 = 4 \times 9$
• Apr 17th 2008, 08:22 PM
Jen
Quote:

Originally Posted by helpmee
so n^2-8?
i dont know what to do after that...

I believe that you should end up with $4(n^2-9)$

But don't forget how you factored the $n^2-16$

You remember that one?

Do the same with $n^2-9$
• Apr 17th 2008, 08:24 PM
helpmee
mmkay the other one... 27t^2+18t+9 my teacher said its (x-1)(3x+1)...
• Apr 17th 2008, 08:29 PM
Jen
$9(t-1)(3t+1)=27t^2-18t-9$ Which is a bit different than the one we started with.
• Apr 17th 2008, 08:31 PM
helpmee
?? so hes wrong??
• Apr 17th 2008, 08:33 PM
Jen
Quote:

Originally Posted by helpmee
??

You said the original problem was $27t^2+18t+9$

Your instructor's factoring would give us $27t^2-18t-9$

Were they supposed to be negative? Did you write the problem down wrong?
• Apr 17th 2008, 08:38 PM
helpmee
hmm so whats the correct factoring? becuase heres his reasoning...

27t^2+18t+9

so

3t^2-2t+1

and then you do

(1x-1) (3x+1)

and thats because FOIL

so -1x(3x)=-3x
and -1(1)=2x
so the answer when you put them together is -2 which is in the 3t^2+18t+9...

i dont get that...does it make sense?

and no i DID copy it right thats why im so confused too..
• Apr 17th 2008, 09:55 PM
o_O
How did the negative sign appear randomly?

$27t^{2}{\color{red}+}18t + 9 = 9\left(3t^{2} {\color{red}+} 2t + 1\right)$

which can't be factored.