SOLUTION: Show that cos18° = [sqrt(10 + 2sqrt5)]/4

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Question 1145897: Show that cos18° = [sqrt(10 + 2sqrt5)]/4
Answer by Alan3354(69443) About Me  (Show Source):
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Show that cos18° = [sqrt(10 + 2sqrt5)]/4
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Use the sin(18)
Then, cos(18) = sqrt(1 -sin^2(18))
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Or, sin(18) = 2sin(9)*cos(9)