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