((x^3-y^3)-3xy(x-y))xy/(y-x)=(x-y)(x^2+y^2-2xy)*xy/(y-x)=-xy(x-y)^2=
=-7*2*2(5sqrt(2))^2=-7*4*25*2=-1400
((x^3-y^3)-3xy(x-y))xy/(y-x)=(x-y)(x^2+y^2-2xy)*xy/(y-x)=-xy(x-y)^2=
=-7*2*2(5sqrt(2))^2=-7*4*25*2=-1400