问题描述: 先化简再求值,3m^2-mn/9m^2-6mn+n^2其中m=3n 1个回答 分类:数学 2014-12-03 问题解答: 我来补答 3m^2-mn/9m^2-6mn+n^2=m(3m-n)/(3m-n)^2=m/(3m-n)=3n/(9n-n)=3/8 展开全文阅读