Why the series is divergent, but the equation holds? $$\sum\limits_{i=1}^{\infty }{\sin kx}=\frac{1}{2}\cot \left( \frac{x}{2} \right)$$
2026-05-14 11:32:50.1778758370
A small question on fourier series
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Because you assumed that the series from which you derived it could be differentiated, when it could not.