y=cos^2(2-1)可看成y=u^2,u=cosv,v=x-1复合而成（考查多个中间变量的复合函数的导数）Yx'=2cos(x-1)·[cos(x-1)]'=2cos(x-1)·[-sin(x-1)]·（x-1)'= -2cos(x-1)sin(x-1)·1= -2cos(x-1)sin(x-1)再由公式sin2a=2sina...