Convergence of an Integral with Increasing Exponent

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SUMMARY

The discussion centers on evaluating the limit of the integral lim n → ∞ ∫ sin(π*x^n) dx from 0 to 1/2. Participants reference Lebesgue's Dominated Convergence Theorem, noting that while x^n converges to zero for x in [0, 1/2], the function sin(π*x^n) does not converge pointwise over the entire domain. The consensus is that the limit can be moved inside the integral for the specified range, alleviating concerns about convergence outside of [0, 1/2].

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Homework Statement


lim n \rightarrow\inf \int sin(pi*x^{n})dx
...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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