x²-x-x²+y=-3y-x=-3(x-y)²=9
x(x-1)-(x²-y）=-3x^2-x-x^2+y=-3y-x=-3x-y=3x²+y²-2xy=(x-y)^2=9
x（x-1)-(x²-y）=-3x^2-x-x^2+y=-3x-y=3x²+y²-2xy=(x-y)^2=3^2=9
