x²+xy=3,xy+y²=-2相减x²+xy-xy-y²=3+2x²-y²=5x²+xy=3(1)xy+y²=-2 (2)(2)*3+(1)x²+xy+3xy+3y²=3-6x²+4xy+3y²=-3（1）*2-(2)*32x²+2xy-3xy-3y²...