(n-m)(n-m)(n-m)/(m-n)(m-n)(m-n) = - (m-n)(m-n)(m-n)/(m-n)(m-n)(m-n) = -1
m-n是n-m 的相反数阿
(n-m)(n-m)(n-m)/(m-n)(m-n)(m-n)=(n-m)/(m-n)=-1