cos-pi-9-cos-2pi-9-cos-4pi-9-

Question Number 85582 by jagoll last updated on 23/Mar/20

\cos (\frac{π}{9}) + \cos (\frac{2 π}{9}) + \cos (\frac{4 π}{9}) =

Commented by som(math1967) last updated on 23/Mar/20

2 c o s (\frac{π}{9})