Show $\displaystyle \lim_{x \to \infty} \frac{50x^{10}+100}{x^{11}+x^6+1}=0$

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Discussion Overview

The discussion revolves around evaluating the limit $\displaystyle \lim_{x \to \infty} \frac{50x^{10}+100}{x^{11}+x^6+1}$, focusing on the methods for determining limits of rational functions as $x$ approaches infinity. Participants explore different approaches and reasoning related to polynomial degrees.

Discussion Character

  • Mathematical reasoning
  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant initially attempts to evaluate the limit but arrives at an incorrect conclusion of 50, expressing frustration about the mistake.
  • Another participant suggests that to find the limit of a fraction of polynomials as $x \to +\infty$, one should focus on the terms of the highest degree, leading to the conclusion that the limit is 0.
  • A similar point is reiterated by a different participant, emphasizing the same approach of considering only the leading terms of the polynomials.
  • There is a question raised about when it is appropriate to divide by the highest power in the limit evaluation process.
  • A participant acknowledges their earlier algebraic error and provides a corrected evaluation of the limit, confirming that it approaches 0.

Areas of Agreement / Disagreement

Participants generally agree on the method of focusing on the highest degree terms to evaluate the limit, but there is no consensus on the initial approach taken by the first participant, which was incorrect.

Contextual Notes

Some participants discuss the method of dividing by the highest power, indicating that this approach can yield the same result, but the specifics of when to apply it remain somewhat unclear.

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How do you show that $\displaystyle \lim_{x \to \infty} \frac{50x^{10}+100}{x^{11}+x^6+1}=0$

What I tried:

$\displaystyle \lim_{x \to \infty} \frac{50x^{10}+100}{x^{11}+x^6+1} =\lim_{x \to \infty} \frac{50+100/x^{11}}{1+1/x^{5}+1/x^{11}} = \frac{50+0}{1+0+0} = 50.$

But this is wrong. (Angry)
 
Last edited:
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If you have a fraction of polynomials and you want to find the limit as $x \to +\infty$ you look only at the terms of largest degree.

So your limit is equal to $\lim_{x \to +\infty} \frac{50 x^{10}}{x^{11}}=\lim_{x \to +\infty} \frac{50}{x}=0$
 
evinda said:
If you have a fraction of polynomials and you want to find the limit as $x \to +\infty$ you look only at the terms of largest degree.

So your limit is equal to $\lim_{x \to +\infty} \frac{50 x^{10}}{x^{11}}=\lim_{x \to +\infty} \frac{50}{x}=0$
Thanks. When is it that we divide the highest power then?
 
Guest said:
Thanks. When is it that we divide the highest power then?

You could also divide by the highest power in this case, if you would want to. The result will be the same...
 
evinda said:
You could also divide by the highest power in this case, if you would want to. The result will be the same...
I get it now - my algebra was wrong in the original post.

$\displaystyle \lim_{x \to \infty} \frac{50x^{10}+100}{x^{11}+x^6+1} =\lim_{x \to \infty} \frac{50/x+100/x^{11}}{1+1/x^{5}+1/x^{11}} = \frac{0+0}{1+0+0} = 0$

Thanks, again.
 

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