原式=m^2-4mn+n^2-n^2+3n^2 =m^2-4mn+4n^2-n^2 =(m-2n)^2-n^2 =(m-2n-n)(m-n+n) =m(m-3n) 满意请点右下角的采纳谢,不满意请追问,您的支持是我奋斗的动力