+0  
 
+15
943
14
avatar+2592 

I'm reviewing for Semester exams, and forgive me, but i have forgotten how to factor polynomials greater than quadratic. If someone could please help, it would be appreciated. An example given is X4+3X3-12X2-6X+20

 Dec 16, 2015

Best Answer 

 #2
avatar+129907 
+15

X^4+3X^3-12X^2-6X+20

 

This might be difficult to factor directly.......we can use the Rational Zeros Theorem to [possibly] reduce the polynomial to one of a 2nd or 3rd degree which might be more easily factored

 

The possible factors are all the factors of 20  divided by all the factors of 1

 

1/1  = 1   is not a factor  because it does not produce 0  when substituted into the polynomial

-1/1  = -1    is not a factor for the same reason

2/1 = 2   is a factor because we get a 0 when we substitute it into the polynomial

 

So   using synthetic division, we have

 

 

2  [ 1   3     - 12       -6       20   ]

           2       10       -4      -20

     -------------------------------------

      1   5      -2        -10       0

 

So, this reduces the polynomial to

 

x^3 + 5x - 2x  - 10       which factors as

 

x^2 ( x + 5)  - 2(x + 5)  =

 

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

 

So.....the factorization is

 

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

 

 

 

cool cool cool

 Dec 16, 2015
 #1
avatar+43 
+5

are you kidding me?! everyone knows how to do that!! jk i have no idea what you are talking about 

 Dec 16, 2015
 #2
avatar+129907 
+15
Best Answer

X^4+3X^3-12X^2-6X+20

 

This might be difficult to factor directly.......we can use the Rational Zeros Theorem to [possibly] reduce the polynomial to one of a 2nd or 3rd degree which might be more easily factored

 

The possible factors are all the factors of 20  divided by all the factors of 1

 

1/1  = 1   is not a factor  because it does not produce 0  when substituted into the polynomial

-1/1  = -1    is not a factor for the same reason

2/1 = 2   is a factor because we get a 0 when we substitute it into the polynomial

 

So   using synthetic division, we have

 

 

2  [ 1   3     - 12       -6       20   ]

           2       10       -4      -20

     -------------------------------------

      1   5      -2        -10       0

 

So, this reduces the polynomial to

 

x^3 + 5x - 2x  - 10       which factors as

 

x^2 ( x + 5)  - 2(x + 5)  =

 

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

 

So.....the factorization is

 

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

 

 

 

cool cool cool

CPhill Dec 16, 2015
 #3
avatar+2592 
+5

OH GOD

COMPLETELY FORGOT ABOUT SYNTHETIC DIVISION

YOU JUST SAVED MY EXAM GRADE

Thanks CPhill

 Dec 16, 2015
 #4
avatar+8581 
0

Thanks guys for catching my mistakes today!!! :)

I have not been feeling my 100% best today :'(

crying

 Dec 16, 2015
 #5
avatar+129907 
0

No prob.....S of A

 

 

cool cool cool

 Dec 16, 2015
 #6
avatar+8581 
0

haha, I see what you did there, CPhill

:p

 Dec 16, 2015
 #7
avatar+2592 
0

TOOK ya long enough

JK Haley 

CPhill, Most just refer to me as Spawn btw

 Dec 16, 2015
 #8
avatar+8581 
0

And here i thought we were starting a beautiful friendship!!

(\_(\

 (-.-)

(,,)(,,)

 Dec 16, 2015
 #9
avatar+2592 
0

We do, You remeber that first post I put up tonight.

Karma

 Dec 16, 2015
 #10
avatar+8581 
0

when did karma get me????

 Dec 16, 2015
 #11
avatar+2592 
0

Well, i was implying that i was giving you back the bad Karma

 Dec 16, 2015
 #12
avatar+8581 
0

haha, ohhh.

I may be a blonde, but that does not mean im stupid. :p

Mind is just running slow right now.. ;)

 Dec 16, 2015
 #13
avatar+2592 
0

Didn't mean to imply you were stupid or anything. Sorry

Anyways, i'm calling it a night, got Pre-calc exam and AP exam tomorrow.

Also, my laptop has 20% battery left.

Night CPhill, Melody, and Haley

 Dec 16, 2015
 #14
avatar+8581 
0

no you didnt make me feel stupid :)

Goodnighht!

 Dec 16, 2015

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