Prove 4 COS120 Cos 480 Cos 720 = Cos 360 Share with your friends Share 0 Rishabh Mittal answered this LHS=4 cos 12° cos 48° cos 72°=2 cos 12° cos72°+48°+cos72°-48° Since 2 cos A cos B=cosA+B+cosA-B=2 cos 12° cos 120° +cos 24°=2 cos 12° -12+cos 24°=-cos 12° + 2 cos 12° cos 24°=- cos 12° +cos24°+12°+cos24°-12°=-cos 12° + cos 36° +cos 12°=cos 36°=RHS -1 View Full Answer
