Prove $$\sin\frac\pi7 \cdot \sin\frac{2 \pi}{7}\cdot\sin\frac{3 \pi}{7} = \frac{\sqrt7}{8}$$
I tried using the product to sum identities but those got me nowhere. Any help would be great.
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This seems to be the same question as Evaluation of $\sin \frac{\pi}{7}\cdot \sin \frac{2\pi}{7}\cdot \sin \frac{3\pi}{7}$. I found it using Approach0, for general advice on searching see: How to search on this site? – Martin Sleziak Dec 11 '18 at 02:58