f0(x)=sinxf1(x)=f0'(x)=cosxf2(x)=f1'(x)=-sinxf3(x)=f2'(x)=-cosxf4(x)=f3'(x)=sinx....可以看出,以4为周期进行循环2005/4=501余1而f1(x)=f0'(x)=cosx所以f2005(x)=cosx
cosX