How to Prove a Multivariable Function Converges to a Specific Value?

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Homework Help Overview

The discussion revolves around proving the convergence of the multivariable function \(\frac{(2^x - 1)\sin(y)}{xy}\) to \(\ln(2)\) as both \(x\) and \(y\) approach 0. Participants are exploring the mathematical reasoning behind this convergence in the context of limits and series expansions.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to identify starting points for the proof, with suggestions of using the Squeeze Theorem and exploring special limits. There is a discussion about the behavior of the function as \(y\) approaches 0 before \(x\) and the implications of separating the function into components dependent on \(x\) and \(y\).

Discussion Status

Some participants have expressed confidence in the answer being \(\ln(2)\), while others are focused on the process of proving this assertion. There is a mix of attempts to clarify the reasoning and explore different mathematical properties that may apply, but no consensus has been reached on a definitive method.

Contextual Notes

Participants are navigating the constraints of homework guidelines, which discourage posting without a real attempt at a solution. There is also a mention of using the Maclaurin series as a potential approach to the proof.

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Homework Statement


How do I prove the function ((2^x)-1)sin(y))/(xy) converges to ln(2) in the case of x=0 and y=0..?


Homework Equations





The Attempt at a Solution


Yeah I'm trying to figure out where to start honestly... I know I'm not suppose to post unless I have a real attempt at the solution.. I could BS something but anyone want to point me in the right direction? Squeeze Theorem? Is there some key property I should be aware of?
 
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PsychonautQQ said:

Homework Statement


How do I prove the function ((2^x)-1)sin(y))/(xy) converges to ln(2) in the case of x=0 and y=0..?


Homework Equations





The Attempt at a Solution


Yeah I'm trying to figure out where to start honestly... I know I'm not suppose to post unless I have a real attempt at the solution.. I could BS something but anyone want to point me in the right direction? Squeeze Theorem? Is there some key property I should be aware of?

Why do you think the answer is ##\ln 2##? Try some special limits to get a feel for it. What if ##y\rightarrow 0## before ##x##, for example.
 
the answer is ln(2), the question says that, we just have to PROVE it is.
 
Yes, the answer is indeed ln(2) I used mclaurin series to prove it.
 
PsychonautQQ said:

Homework Statement


How do I prove the function ((2^x)-1)sin(y))/(xy) converges to ln(2) in the case of x=0 and y=0..?


Homework Equations





The Attempt at a Solution


Yeah I'm trying to figure out where to start honestly... I know I'm not suppose to post unless I have a real attempt at the solution.. I could BS something but anyone want to point me in the right direction? Squeeze Theorem? Is there some key property I should be aware of?

Your function is a function of x only times a function of y only:
[tex] \frac{(2^x - 1)\sin y}{xy} = \frac{2^x - 1}{x} \frac{\sin y}{y}[/tex]

One can show that if [itex]\lim_{x \to 0} f(x)[/itex] and [itex]\lim_{y \to 0} g(y)[/itex] exist then
[tex] \lim_{(x,y) \to 0} f(x)g(y) = \left(\lim_{x \to 0} f(x) \right)\left( \lim_{y \to 0} g(y) \right)[/tex]

Also remember that
[tex] \lim_{x \to 0} \frac{f(x) - f(0)}x = f'(0)[/tex]
assuming the limit exists.
 

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