若xy=m,且1/x^2+1/y^2=n,则(x-y)^2=_______
问题描述：
若xy=m,且1/x^2+1/y^2=n,则(x-y)^2=_______
如题
答
(1/x-1/y)^2= 1/x^2+1/y^2-2/xy
(y-x)^2/(yx)^2= 1/x^2+1/y^2-2/xy
(x-y)^2/m^2= n-2/m
(x-y)^2 = nm^2-2m