首先 Cos(2x) = Cosx ^2 - Sinx^2= Cosx^2 -1 + Cosx^2=> Cosx^2 = 1/2 ( 1 + Cos (2x))所以1/2 积分号:(0 - 2π) x + xcos 2x这样你会了吧?x直接积即可,后面部分用分部积分V" = Cos (2x)u = X...