Please prove or disapprove this equality

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SUMMARY

The equality sum_(n in Z)e^(2 pi i n s) = 2 delta(s) is proven to be false. The correct formulation, based on Fourier series, is sum_{n in Z} delta(s-n). The discussion highlights that the sum does not converge due to the behavior of the exponential function as n approaches infinity, specifically that lim_{n→∞} e^(2 pi i n s) does not equal zero. This conclusion is supported by the properties of the delta function and Fourier series expansion.

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bayes
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Please help me prove or disapprove the following equality:

sum_(n in Z)e^(2 pi i n s) = 2 delta (s)

Z is the set of integers and s any variable and delta is the usual delta function that is 0 when s is different from 0 and infinite if s is 0.

Thanks
 
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I think it's false.

Based on Fourier series I think the RHS of that equality should, [instead of 2 delta(s)], read:

[tex]\sum_{n\,\, \mbox{\rm in Z}} \delta(s-n)[/tex]

Hint : Consider the Fourier series expansion of the above (period=1) function of s.
 
Last edited:
By what you wrote above did you mean

[tex]\sum^{\infty}_{n=-\infty} e^{2 \pi i n s}[/tex]

This sum doesn't converge because [tex]lim_{n\rightarrow\infty}e^{2 \pi i n s}\neq0[/tex]
 

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