Trouble Factoring X^4-15X^3+32X+372X-1440)/X^2-X-30

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Discussion Overview

The discussion revolves around the factoring of the polynomial expression (X^4-15X^3+32X+372X-1440)/X^2-X-30 as X approaches 6. Participants explore methods for simplifying the expression and addressing the indeterminate form encountered when substituting X with 6.

Discussion Character

  • Homework-related, Mathematical reasoning, Technical explanation

Main Points Raised

  • One participant expresses difficulty in factoring the polynomial and requests assistance for a manual solution.
  • Another participant suggests that the root factor theorem indicates that if x=6 is a root, then x-6 is a factor.
  • A different participant questions the correctness of the original expression and proposes a corrected version, leading to a factorization that simplifies the expression as X approaches 6.
  • One participant acknowledges the correctness of the assumption made by another regarding the factorization.
  • A later reply introduces L'Hopital's rule as an alternative method to resolve the indeterminate form, suggesting it may be less work than polynomial long division.

Areas of Agreement / Disagreement

Participants generally agree on the application of the root factor theorem and the factorization approach, but there is some uncertainty regarding the original expression's accuracy. The discussion remains unresolved regarding the best method to approach the problem.

Contextual Notes

There is a potential ambiguity in the original polynomial expression, particularly concerning the terms involved, which may affect the factoring process. The discussion also highlights the existence of multiple methods to address the indeterminate form.

MattsAli1108
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(X^4-15X^3+32X+372X-1440)/X^2-X-30 as X approaches 6

I know that somehow I am supposed to be able to factor this, but I'm having trouble doing so, and am stuck with a TI-82 that isn't very much help, either. Could someone please show me how to do this by hand?
 
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EDIT: Sorry, I was blind to the answer. mathwonk has it right in the next post...
 
Last edited:
the root factor theorem says that if x=6 makes a polynomial zero, then x-6 is a factor, and vice versa.
 
MattsAli1108 said:
(X^4-15X^3+32X+372X-1440)/X^2-X-30 as X approaches 6
did you write the question correctly?
is the third term in the numerator 32x^2?
then it becomes
\frac{x^4-15x^3+32x^2+372x-1440}{x^2-x-30}=\frac{(x+5)(x-8)(x-6)^2}{(x+5)(x-6)}=(x-8)(x-6)

and this approaches 0 as x approaches 6.
 
I would have a feeling you assumption is correct, murshid. Nice work
 
Thank you so much for your help! All of you! It is very much apprecitated!
 
Since the trouble was originally that you got 0/0 by plugging 6 in directly, you could also have used L'Hopital's rule. Of course, it is conceptually more elementary to factor the polynomial, but it may actually be less work to do 1 derivative than to do the polynomial long division.

Just offering an alternative.

--Stuart Anderson
 

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