Is this equality valid? I just noticed it, and I haven't heard of it before.

$\displaystyle 2cos(\frac{\pi }{5})=\varphi,~where~\varphi~is~the~golden~ratio. $

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- Jul 3rd 2011, 02:14 AMscoungedAbout the golden ratio
Is this equality valid? I just noticed it, and I haven't heard of it before.

$\displaystyle 2cos(\frac{\pi }{5})=\varphi,~where~\varphi~is~the~golden~ratio. $ - Jul 3rd 2011, 02:33 AMmr fantasticRe: About the golden ratio
Found using Google in t < 60 seconds:

http://www.theproblemsite.com/thegol...igonometry.asp

Golden ratio and special angles — The Endeavour