2m-n/2mn : n-2m/m^2-n^2 = 2m-n/2mn : 2m-n/n^2-n^2 = (2m-n)(m^2-n^2)/2mn(2m-n) = n^2-m^2/2mn = (n-m)(n+m)/2mn
2m-n/2mn : n-2m/m^2-n^2 = 2m-n/2mn : 2m-n/n^2-n^2 = (2m-n)(m^2-n^2)/2mn(2m-n) = n^2-m^2/2mn = (n-m)(n+m)/2mn