2x²-xy-3y²=0(x+y)(2x-3y)=0x=-y,2x=3yx≠-y所以y=(2/3)x原式=(x²+2/3*x²)/(2/3*x²-4/9*x²-x²)=-15/7
2x^2-xy-3y^2=0得（2x-3y)(x+y)=0∵x≠y,∴x=1.5y,将之代入即可
