f'(x)=（-x)'-(ln(-x))'
=-1-(1/(-x))*(-1)
=-1-1/x
或
设y=-x
df(x)/dx=(df(x)/dy)*(dy/dx)
=(d(-x-ln(-x))/dy)*(dy/dx)
=(d(y-lny)/dy)*((dy/dx)
=(1-1/y)*(-1)
=(1+1/x)*(-1)
=-1-1/x