factoring trinomials

[idgit_chik]

i NEED help with factoring trinomials of the type ax^2+b+c

the question is 6x^2-15x-21

 

[Guest]

So first of all, you might think. What are the numbers that make up 6, and what are the numbers that make up 21?

You might want first list them all out.
6: 1,2,3,6
21: 1,3,7,21

So you might think now which numbers from that list would give you 15... hmm... Think about it. There is a solution. If you don't get it, post a reply. The answer is just there. lol. =].

 

[soroban]

Hello, idgit_chik!

Factor: $\displaystyle \,6x^2\,-\,15x\,-\,21$

First, factor out a 3 . . .

$\displaystyle \;\;6x^2\,-\,15x\,-\,21\;=\;3(2x^2\,-5x\,-\,7)$

The trinomial is still tricky: $\displaystyle \,3(x\,+\,1)(2x\,-\,7)$


But always remember Rule #1: $\displaystyle \:\text{Look for common factors.}$

 

[idgit_chik]

well thanx ppl but the stuff you have down is stuff i already no!!!

what comes after the factor the 3............................me confused after that!!! :?

 

[idgit_chik]

and my teacher taught me to use FOIL when solving these trinomials.................so does ne one know how to solve it that way.........................................

 

[tkhunny]

Watch your language!! :wink:

"FOIL" is a crutch substitute for simply learning how to multiply. It never will help you factor. Multiplication, on the other hand, will help you check your factoring - proving that your factorization reproduces the original expression.

 

[idgit_chik]

hey ppl guess what i think i got the answer!!! :lol:

i got 3(2x-7) (x+1) for my final answer...........plz tell me if im right.............PLEASE!!!! :roll:

 

[skeeter]

hey ppl guess what i think i got the answer!!! :lol:

i got 3(2x-7) (x+1) for my final answer...........plz tell me if im right.............PLEASE!!!! :roll:

do you even read the responses to your posts? check out Soroban's response ...
thoroughly.

 

[idgit_chik]

OOPS!!!

sorry i had another blonde moment!!!

i didnt know that was the answer................hehe i thought that was...........nvm
oh well no i no i got the right answer...............

hehe :lol: :roll:

 

[stapel]

the stuff you have down is stuff already [know]!!

This is why it is asked that posters show their work. Otherwise, the tutors are perfectly correct to assume that the poster can't even get started.

So in future posts, kindly please reply showing your work, and then please read the replies you receive.

Thank you for your consideration.

Eliz.