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I'm reseaching a problem that lead me to evaluating the product $$\prod\limits_{k=1}^{[n/4]} \tan \dfrac{k\pi}{n}=?,$$ I can evaluate $$\prod\limits_{k=1, k\neq \frac{n}{2}}^{n}\vert \tan \dfrac{k\pi}{n}\vert=\left\{ \begin{array}{l}n, n \text{ is odd} \\ 1, n\text{ is even} \end{array}\right.,$$ but i can't solve the above product, please. Thanks a ton.

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