Can L'Hopital's Rule be used to solve (0/0)^infinity limits?

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Homework Help Overview

The discussion revolves around evaluating limits of the form (0/0)^infinity, specifically through the lens of L'Hôpital's Rule and related techniques. Participants explore the nuances of applying L'Hôpital's Rule to a limit involving an exponential expression.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of L'Hôpital's Rule and whether to consider the power of 1/x^2 during differentiation. There are suggestions to take the natural logarithm of the expression to simplify the limit evaluation. Some participants express uncertainty about the necessity of L'Hôpital's Rule versus other methods like Taylor expansions.

Discussion Status

The conversation is active, with various approaches being considered. Some participants suggest that taking the logarithm of the expression may lead to a clearer path for evaluation, while others emphasize the relevance of L'Hôpital's Rule as indicated in the thread title. There is no explicit consensus on the best approach yet.

Contextual Notes

Participants are navigating the complexities of limits involving indeterminate forms and are considering the implications of different mathematical techniques. The discussion reflects a mix of familiarity with the topic and uncertainty about the most effective methods to apply.

Crystal037
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Homework Statement
lim x tends to 0 (((e^x+e^(-x)-2)/(x^2))^(1/x^2))
Relevant Equations
lim x tends to 0 (e^x-1)/x=1
It is of the form (0/0)^infinity. I know how to solve 1^infinity form
 
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Is it ##\lim_{x \to 0} \left( \dfrac{e^x+e^{-x}-2}{x^2}\right)^{\frac{1}{x^2}}\,?##

For L'Hôpital you will have do calculate the derivatives of numerator and denominator.
 
Yes but should i consider the power 1/x^2 while differentiating the numerators and denominator
 
I would take it for both: ##\left( e^x+e^{-x} - 2\right)^{x^{-2}}## and ##\left( x^2 \right)^{x^{-2}}##. If I'm right, then the limit without the power of ##\frac{1}{x^2}## is ##1##, but with it, it isn't. But I'm not sure whether L'Hôpital will do. Maybe it needs more effort and a few Taylor expansions.
 
fresh_42 said:
I would take it for both: ##\left( e^x+e^{-x} - 2\right)^{x^{-2}}## and ##\left( x^2 \right)^{x^{-2}}##. If I'm right, then the limit without the power of ##\frac{1}{x^2}## is ##1##, but with it, it isn't. But I'm not sure whether L'Hôpital will do. Maybe it needs more effort and a few Taylor expansions.
I wouldn't do things this way. Instead, I would let ##y = \left(\frac{ e^x+e^{-x} - 2}{x^2}\right)^{1/x^2}##, take ln of both sides, and then take the limit. The result you get, if a limit exists will be the limit of the ln of that expression, so the final answer is obtained by exponentiating.

I haven't worked the problem, but this is the usual approach when dealing with limits with some expression raised to a variable power.
 
Yes, but L'Hôpital was given in the thread title.
 
fresh_42 said:
Yes, but L'Hôpital was given in the thread title.
The limits after taking the log can be evaluated using the Hospital rule. According to Mathematica, the limit is equal to ##e^{1/12}##.

You can simplify the algebra by using the fact that
$$\frac{e^x + e^{-x} - 2}{x^2} = \frac{(e^{x/2} - e^{-x/2})^2}{x^2} = \left[\frac{\sinh (x/2)}{x/2}\right]^2.$$ I had to apply L'Hopital's rule several times and eventually arrived at the correct result.
 
fresh_42 said:
Yes, but L'Hôpital was given in the thread title.
My response didn't preclude using L'Hopital's Rule in evaluating the limit.
 

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