Is the Limit of x^n/e^x Equal to 0 for Negative Integers?

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Discussion Overview

The discussion centers on the limit of the expression \( \frac{x^n}{e^x} \) as \( x \) approaches infinity, specifically for negative integer values of \( n \). Participants explore the implications of applying L'Hôpital's rule and the interpretation of limits involving zero.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether \( \lim_{x \to \infty} \frac{x^n}{e^x} = 0 \) for negative integers \( n \) and seeks clarification on the expression \( (->\infty)0 = 1 \).
  • Another participant suggests using L'Hôpital's rule for limits that yield an indeterminate form, stating that the derivatives of the numerator and denominator will lead to a definitive answer.
  • A later reply asserts that for any fixed negative integer \( n \), the limit will always be 0, as \( e^x \) grows faster than \( x^n \) after taking derivatives.
  • Clarification is provided regarding the definition of negative integers, with \( n \) specified as \( \{-1, -2, -3, -4, \ldots\}.
  • Another participant rephrases the expression, indicating that \( \frac{x^n}{e^x} \) for negative \( n \) can be rewritten as \( \frac{1}{x^{-n} e^x} \), and argues that since both \( x^{-n} \) and \( e^x \) grow without bound, the limit approaches 0.
  • Concerns are raised about the expression \( (->\infty)0 \), with one participant stating that the limit could either be 0 or a non-zero number, thus complicating the interpretation of \( 0^0 \).

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of limits involving zero and the application of L'Hôpital's rule. While some assert that the limit approaches 0, others raise questions about the validity of certain expressions and the conditions under which limits are evaluated. The discussion remains unresolved regarding the implications of \( (->\infty)0 \).

Contextual Notes

Limitations include potential misunderstandings of mathematical notation and the conditions under which L'Hôpital's rule applies. The discussion does not resolve the ambiguities surrounding the expression \( (->\infty)0 \) and its implications.

phymatter
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is limx->infinity xn/ex =0 for n = -ve integers , if yes then why?
also is (->infinity)0 =1 ?
 
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You know if you get inifinity over infinity you must "change" your fractionexpression by using L'hopitas rule. It says that if you either get infinity over ifinity or zero over zero you must derive nominator og denominator so that you get a fractionexpression which is capable of giving you an answer by substituting the variable x.
 


phymatter said:
is limx->infinity xn/ex =0 for n = -ve integers , if yes then why?
also is (->infinity)0 =1 ?

I don't know what you mean by n = -ve integers. However using L'Hopital's rule for any fixed n, the result will always be 0. ex will persist as you take derivatives, while xn will be 0 after n derivatives.
 


mathman said:
I don't know what you mean by n = -ve integers.
by n = -ve integers i mean that n={-1,-2,-3,-4,...}
 


phymatter said:
is limx->infinity xn/ex =0 for n = -ve integers , if yes then why?
also is (->infinity)0 =1 ?
Surely it is not that difficult to write "negative"!

In any case, it should be obvious that x^n/e^x, for n negative, is the same as 1/(x^ne^x) with n positive. And since both x^n and e^x grow without bound as x goes to infinity, the fraction goes to 0.

Again (->infinity) makes no sense. If you mean \lim_{x\to\infty}f(x) it still makes no sense because that limit might be 0, in which case 0^0 is not defined, or that limit might be a non-zero number, in which case the limit is 1.
 

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