x²+xy-(xy-y²)=x²+xy-xy+y²=x²+y²=2-(-7)=9x²+y²=9 x²+xy+2(xy-y²)=x²+xy+2xy-2y²=x²+3xy-2y²=2+2x(-7)=-12 x²+3xy-2y²=-12
