今晚先回答的问题：雅安平安!
n/(m-n) x (m^3+mn^2-2m^2n)/(n^3)÷(n^2-m^2)/(mn+n^2)
=n/(m-n) x m(m-n)²/(n^3)÷(n-m)(m+n)/n(m+n)
=[n²m(m-n)²]/[(m-n)n³(n-m)]
=[-m(m-n)²]/[(m-n)²n]
=[-3x1]/[2]
=-3/2