prove- cos2(pi /8) + cos2 (3pi / 8) +cos2(5pi / 8) +cos2 (7pi / 8) = 2 Share with your friends Share 7 Ankush Jain answered this To prove:Proof:[Hence proved] 66 View Full Answer Arvind Mandal answered this cos2 pi/8 +cos2 3pi/8 +cos2 pi/2+pi/8 +cos2 pi/2+3pi/8 =cos2 pi/8 +cos2 3pi/8 +sin2 pi/ 8+sin2 3pi/8 =2 -29