m>n>0,则有m^2-n^2>0
是否是m^2+n^2=4mn?
(m^2-n^2)^2=(m^2+n^2)^2-4m^2n^2=16m^2n^2-4m^2n^2=12m^2n^2
故m^2-n^2=2根号3 mn
即(m^2-n^2)/mn=2 根号3