What is the Method for Factoring Polynomials with Limits?

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Discussion Overview

The discussion revolves around the method for factoring polynomials in the context of evaluating limits, specifically focusing on the limit of the function f(x) = (x + 2) / (x^3 + 8) as x approaches -2. Participants explore different approaches to factoring polynomials and applying limit laws.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant, Susan, seeks help with finding the limit of f(x) as x approaches -2, expressing difficulty in factoring the polynomial.
  • Another participant questions whether the expression a^3 - b^3 can be factored, suggesting a focus on a^3 + b^3 instead.
  • A participant clarifies that the function should be considered as f(x) = (x + 2) / (x^3 + 8), indicating the need to factor a sum of cubes.
  • There is a discussion about the equivalence of factoring a^3 + b^3 and a^3 - (-b)^3, with one participant suggesting that familiarity with the difference of cubes may help spark understanding.
  • One participant emphasizes the importance of a direct approach in teaching, acknowledging that students may struggle with connections due to various factors like nerves or haste.
  • Another participant provides a general rule that if a polynomial is zero at x = a, it must have a factor of (x - a), illustrating this with the example of x^3 + 1 having (x + 1) as a factor.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method for factoring the polynomial or applying limits, as multiple approaches and perspectives are presented without resolution.

Contextual Notes

There is an assumption that participants are familiar with polynomial factoring and limit evaluation, but specific steps or methods for applying these concepts to the given function remain unresolved.

susan__t
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the question is:

The limit as x approaches -2 when f(x)= x+2/x3+8

I cannot factor it, or use a limit law (to my knowledge) and am simply having trouble finding the answer which is suppose to be 1/12.

Any help getting me started would be greatly appreciated

Susan
 
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Can you factor a^3 - b^3?
 
Actually, you need to factor

[tex] a^3 + b^3[/tex]

instead of the difference of two cubes (assuming your function is

[tex] f(x) = \frac{x+2}{x^3 + 8}[/tex]
)
 
It's the same thing, because a^3 + b^3 = a^3 - (-b)^3. :wink:

The reason I chose to use difference instead of sum is because difference is usually more familiar, and might spark the right idea.
 
Certainly true and obvious when you know the steps that are to be done. I've been teaching mathematics and statistics long enough to realize that occasionally a student may not make that connection - not because of lack of ability, but because of frustration, nerves, haste, or many other reasons. In a situation like this, a little more direct approach can't hurt.
My previous post was not intended to be smarmy - I hope that no offense was taken, because none was meant.
 
thank you so much both of you, I really had no idea what I could branch out of the equation and I would never have found that on my own
 
You are welcome Susan_t. Good luck with your studies.
 
WHENEVER a polynomial is 0 at x= a, then it has a factor of (x-a). Since x3+ 1 is 0 at x= -1, it MUST have (x+1) as a factor. Divide x3+ 1 by x+ 1 to find the other factor (which is, of course, x2+ x+ 1).

Notice that says that any time you have a ratio of polynomial and both numerator and denominator are 0 at x= a, each MUST have a factor of x-a which you can then cancel.
 

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