I am trying to prove that cos(pi/5)= (1+sqrt(5))/4
I tried finding the 5th roots of unity and then just using the real part cis(pi/5) but then i dont know how to get it = (1+sqrt(5))/4.
I am stuck somewhere here.
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See here: Trigonometry Angles--Pi/5 -- from Wolfram MathWorld
i am still confused though. that website is for sin(pi/5) i let x=cos(theta) and now i have (x+y)^5 and i expanded it out. but now i am still stuck.
nzmathman has shown you how to find . Now use , taking the positive square root.
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