I want to show that $\sum_{n=-\infty }^{+\infty }\frac{1}{(n+\alpha )^{2}}=\frac{\pi ^{2}}{(\sin\pi \alpha )^{2}}$, the introduction to the Poisson summation formula is in this link https://en.wikipedia.org/wiki/Poisson_summation_formula, I want to show this by using Poisson summation formula, the hint of this exercise says we can check the function $g$ such that $g=1-|x|$when $|x|\leq 1$ and $g=0$ otherwise, the Fourier transform of g is $F(g)(\xi)=(\frac{\sin(\pi \xi)}{\pi \xi })^{2}$, so how to use g and Poisson summation formula to prove it ? Can anyone help me, thank you in advance
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I have written the names with capitals: Poisson, Fourier... – Jean Marie Dec 01 '21 at 10:27
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I have corrected it @DavidC.Ullrich – YuerCauchy Dec 01 '21 at 11:02
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please undo the downvote – YuerCauchy Dec 01 '21 at 11:02
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Please show your work. What have you tried? What hard moments did you encounter? – openspace Dec 01 '21 at 11:05
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See this answer by Mhenni Benghorbal: https://math.stackexchange.com/q/208407 – Jean Marie Dec 01 '21 at 11:12
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This has already been asked plenty of times, see here and here – K.defaoite Dec 01 '21 at 11:25
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The coments are misleading, the OP wants to use the Fourier transform of $\sin^2 x /x^2$ not $1/(x+a)^2$ – reuns Dec 01 '21 at 13:03
1 Answers
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You want to prove that $$\sum_{n=-\infty }^{+\infty }\frac{\sin^2(\pi (n+\alpha))}{\pi^2(n+\alpha )^{2}}=1=\sum_k e^{2i\pi \alpha k}g(k)$$

reuns
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