[(5x-4)-x]/(x-1)=(4x-4)/(x-1)=4(x-1)/(x-1)=4所以lim((5X-4)-X)÷(X-1)＝lim[(5x-4)-x]/(x-1)=lim(4x-4)/(x-1)=lim4(x-1)/(x-1)=lim4＝4
