当3m=2n,z则(m/m+n)+(n/m-n)-(n2/m2-n2)等于多少?
问题描述：
当3m=2n,z则(m/m+n)+(n/m-n)-(n2/m2-n2)等于多少?
答
3m=2nm=2n/3m/(m+n)+n/(m-n)-(n^2)/(m^2-n^2)=[m(m-n)+n(m+n)]/(m^2-n^2)-(n^2)/(m^2-n^2)=(m^2+n^2)/(m^2-n^2)-(n^2)/(m^2-n^2)=m^2/(m^2-n^2)=[4(n^2)/9]/[4(n^2)/9-n^2]=-4/5