So here is my problem,
I would like to prove an identity I found in a book which was given without a proof.
Namely $$-i\sum_{n\in\mathbb Z} \operatorname{sign}(n)\cdot e^{i2\pi nx}=\cot(\pi x)$$ I thought since there is no explicit proof it would be easy to show it but I failed...
Could someone help me? Or does anybody know where I can find the proof?
Thank you!