(x-y)^2=(x+y)^2-4xy=m^2-4n x^2+y^2=(x+y)^2-2xy=m^2-2n,3,(x-y)^2=(x+y)^2-4xy=m^2-4n x^2+y^2=(x+y)^2-2xy=m^2-2n,2,
