Hey, I have a question, you can factor using guess and check or grouping, here it is

-13a + 12 - 4a^2

the answer is -(a+4)(4a-3)

Not sure how to get it using either one, please help! Thanks!

Printable View

- January 13th 2008, 09:20 PMMathMackFactoring polynomials
Hey, I have a question, you can factor using guess and check or grouping, here it is

-13a + 12 - 4a^2

the answer is -(a+4)(4a-3)

Not sure how to get it using either one, please help! Thanks! - January 13th 2008, 10:02 PMjanvdl
First re-arrange:

Now factor out the negative sign

Now we should take the term and factorise that, keeping in mind that it is not yet complete. (The and terms represent the constants)

Now we should see which constants give us a product of 12.

(1 x 12 ; 2 x 6 ; 3 x 4)

Now from those options we should find which also satisfies the middle term.

Can you take it from here? Just do it step by step. - January 13th 2008, 10:03 PMMathMack
I also have 4 more, any help is appreciated!

2.) n^3-n^2+n-1

3.) 4a(a+2) - 8 (a+2)

4.) -6x^3 +10x^2 - 4x^4

5.) a rectangle has area described by the polynomial 6x^2 + x -1 suare centimeters. Find the length and width of the rectangle. Thanks again - January 13th 2008, 10:08 PMMathMack
kinda still stuck on that first one. Thanks for your help

- January 13th 2008, 10:11 PMjanvdl
- January 13th 2008, 10:12 PMjanvdl
- January 13th 2008, 10:15 PMMathMack
I got the part where you take the negative out, but after that i'm lost, I know it's (4a something)(a something) but lost to go after that, I know you must find factors but not sure

- January 13th 2008, 10:24 PMjanvdl
- January 13th 2008, 10:25 PMMathMack
and the answers in the back of the book for the problems you answered are a little different, thanks for helping me, i'm just confused!

2.) n^3-n^2+n-1

(n-1) (n^2 +1)

3.) 4a(a+2) - 8 (a+2)

4(a+2)(a-2)

4.) -6x^3 +10x^2 - 4x^4

-2x^2(2x+5)(x-1)

5.) a rectangle has area described by the polynomial 6x^2 + x -1 suare centimeters. Find the length and width of the rectangle.

2x-5 - January 13th 2008, 10:27 PMjanvdl
- January 13th 2008, 10:30 PMMathMack
yes and on the first one we worked on they have the answer -(a+4) (4a-3)

Still lost on that one

THANKS JANVDLL! - January 13th 2008, 10:39 PMjanvdl
- January 13th 2008, 10:41 PMMathMack
that's what i'm not sure on either, the part that we should find two numbers for is positive 12

- January 13th 2008, 10:45 PMjanvdl
- January 13th 2008, 10:54 PMMathMack
okay, I finally got that one all figured out completly, just took awhile, The next one I can't figure out is the n^3-n^2 +n -1