Limit of the product of these two functions

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Discussion Overview

The discussion centers on the limit of the product of two functions, specifically when one function approaches zero and the other is a bounded oscillatory function, such as sine. Participants explore the implications of these limits and seek references or theorems that support their claims.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about a theorem that states if ##\lim_{x \to \infty}f(x)=0## and ##g(x)=\sin x##, then ##\lim_{x \to \infty}f(x)g(x)=0##, suggesting that this might hold true for functions as well as sequences.
  • Another participant asserts that if ##g## is any bounded function, an epsilon-delta proof can be applied to demonstrate the limit.
  • A different participant notes that the absolute value of the product ##|f(x)g(x)|## is bounded by ##|f(x)|##, which approaches zero.
  • One participant mentions that while they do not know a specific source for this problem, it relates to the Squeeze theorem, which is commonly found in calculus textbooks.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the existence of a specific theorem that directly addresses the problem, and there are multiple viewpoints on how to approach the limit of the product of the two functions.

Contextual Notes

The discussion highlights the dependence on definitions of boundedness and the conditions under which the limits are evaluated. There is also an acknowledgment of the potential need for further clarification on the application of the Squeeze theorem in this context.

LagrangeEuler
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If we have two functions ##f(x)## such that ##\lim_{x \to \infty}f(x)=0## and ##g(x)=\sin x## for which ##\lim_{x \to \infty}g(x)## does not exist. Can you send me the Theorem and book where it is clearly written that
\lim_{x \to \infty}f(x)g(x)=0
I found that only for sequences, but it should be correct for functions also.
 
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LagrangeEuler said:
If we have two functions ##f(x)## such that ##\lim_{x \to \infty}f(x)=0## and ##g(x)=\sin x## for which ##\lim_{x \to \infty}g(x)## does not exist. Can you send me the Theorem and book where it is clearly written that
\lim_{x \to \infty}f(x)g(x)=0
I found that only for sequences, but it should be correct for functions also.
If ##g## is any bounded function then there is a straightforward epsilon-delta proof.
 
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|f(x)g(x)| is bounded by |f(x)| goes to 0
 
I don't know of a specific place that states this exact problem, but this is an application of the Squeeze theorem which can be found in any calculus textbook.
 

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