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2016 Chandigarh RMO (4cos^2 9^o - 3) (4 cos^2 27^o -3) = tan 9^o

Source:

August 9, 2019
trigonometry

Problem Statement

Prove that (4cos29o3)(4cos227o3)=tan9o(4\cos^29^o – 3) (4 \cos^227^o– 3) = \tan 9^o.