Convergence of an Integral with Increasing Exponent

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    Integral Limit
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Homework Help Overview

The discussion revolves around the convergence of an integral involving the sine function with an increasing exponent, specifically the limit of the integral of sin(pi*x^n) as n approaches infinity, over the interval from 0 to 1/2.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of Lebesgue's Dominated Convergence Theorem and question the pointwise convergence of the function involved. There is also a consideration of u-substitution as a method, although it appears to be unproductive. Some participants question whether the convergence of x^n to zero for x in [0,1/2] is sufficient for the limit to be moved inside the integral.

Discussion Status

The conversation is ongoing, with participants exploring different interpretations of the convergence criteria and the implications of the integral's limits. There is a recognition of the need to focus on the specified domain of integration.

Contextual Notes

There is a mention of potential confusion regarding the necessity of convergence over the entire domain versus just the interval of integration. Participants are navigating the implications of the theorem in the context of the problem's constraints.

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Homework Statement


[tex]lim n \rightarrow\inf \int sin(pi*x^{n})dx[/tex]
...integral is from x=0 to 1/2.


Homework Equations





The Attempt at a Solution


Lebesgue's Dominated Convergence Theorem says that I can move the limit inside, but only if fn converges pointwise to a limit f, which I don't believe it does. Even so, there is no limit as n approaches infinity of fn.
I also tried u substitution, setting u = pi*x^n, but that didn't get me anywhere.

Thanks in advance
 
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Doesn't x^n converge to zero for x in [0,1/2]? Or am I confused?
 
It does, but in order to move the limit inside and use Lebesgue's, doesn't sin(pi*x^n) have to converge to a limit over the entire domain, not just [0,1/2]?
 
Not as far as I know. You are only integrating over [0,1/2]. Why do you have to worry about values outside of that range? Just call the domain [0,1/2].
 
I guess I was over thinking it. Thanks for your help.
 

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