已知3m=4n≠0,则m+n分之m+ m-n分之n -m的二次方-n的二次方分之m的二次方

m/(m+n)+n/(m-n)-m^2/(m^2-n^2)
=m/(m+n)+n/(m-n)-m^2/(m+n)(m-n)
=[m(m-n)+n(m+n)-m^2]/(m+n)(m-n)
=(m^2-mn+mn+n^2-m^2)/(m+n)(m-n)
=n^2/(m+n)(m-n)
=n^2/(m^2-n^2)
3m=4n
9m^2=16n^2
n^2=9/16m^2
n^2/(m^2-n^2)
=[9/16m^2]/(m^2-9/16m^2)
=9/16*16/7
=9/7