7Y(X-3Y)^2-2(3Y-X)^3=(X-3Y)^2(7Y-6Y+2X)=(X-3Y)^2(2X+Y)=6
(X-3Y)^2-2(3Y-X)^3=7Y(3Y-X)^2-2(3Y-X)^3=(3Y-X)^2[7Y-2(3Y-X)]=(3Y-X)^2(7Y-6y+2X)=(3Y-X)^2(2X+Y)=6(-1)^2=6
