设Z=X/2,则Z(x)'=1/2,设U=cos(X/2)=cos Z,U(x)'=U(z)'·Z(x)'=(-sin Z)·(1/2)=-(1/2)sin (X/2)Y=[COS(x/2)]^5=U^5,所以Y(x)'=Y(u)'·U(x)'=(5U^4)·[-(1/2)Sin (X/2)] =[5cos^4 (X/2)]·[-(1/2)Sin (X/2)] ...