原式f(x)=log(1000)x-1000x=(1/3)lgx-1000x
f'(x)=(1/3xln10)-1000
令f'(x)=0
x=(1/3000ln10)
即在x=(1/3000ln10)时最小
f(x)=(1/3)lg3-1-(1/3)lgln10-(1/3)lg10