Question

已知x²+xy﹦2，xy-y²﹦-7,求下列代数式的值 x²+y² x²+3xy-2y²

x²+y²和 x²+3xy-2y²的值

Answer 1

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