arXiv · 0909.5072
We give two proofs of the identity $$\sqrt{\frac{\cos\frac{2π}{5}} {\cos\fracπ{5}}}+\sqrt{\frac{\cos\fracπ{5}} {\cos\frac{2π}{5}} }=\sqrt{5},$$ using and not using the gold ratio.
Vladimir Shevelev. 2009-09-28. Gold ratio and a trigonometric identity. https://arxiv.org/abs/0909.5072
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