分式约分m^2-m^2/m^2+3mn+2n^2

题目

分式约分m^2-m^2/m^2+3mn+2n^2
2.已知a+b=-18,ab=12,求a^2-ab-2b^2/a^2b-2ab^2的值

答案

（1）m^2-m^2/m^2+3mn+2n^2
=(m+n)(m-n)/[(m+n)(m+2n)]
=(m-n)/(m+2n)
(2)a^2-ab-2b^2/a^2b-2ab^2
=(a-2b)(a+b)/[ab(a-2b)]
=(a+b)/ab
=-18/12
=-3/2