(m+2/m²-2m)-（m-1/m²-4m+4）÷（m-1/m）=(m+2)/m(m-2)-(m-1)/(m-2)^2*m/(m-1)=(m+2)/m(m-2)-m/(m-2)^2=[(m+2)*(m-2)-m*m]/m(m-2)^2=(m^2-4-m^2)/m(m-2)^2=-4/m(m-2)^2 m=4=-4/4(4-2)^2=-1/4
