cos-4-pi-9-cos-4-2pi-9-cos-4-3pi-9-cos-4-4pi-9-

Question Number 156321 by cortano last updated on 10/Oct/21

\cos^{4} (\frac{π}{9}) + \cos^{4} (\frac{2 π}{9}) + \cos^{4} (\frac{3 π}{9}) + \cos^{4} (\frac{4 π}{9}) = ?

Commented by john_santu last updated on 10/Oct/21

a n s : \frac{19}{16}