已知2x^2-xy-3y^2=0,且x不等于-y.求x/{y-[x^2/(x-y)]}的值.
问题描述：
已知2x^2-xy-3y^2=0,且x不等于-y.求x/{y-[x^2/(x-y)]}的值.
答
2x²-xy-3y²=0
(x+y)(2x-3y)=0
x=-y,2x=3y
x≠-y
所以y=(2/3)x
原式=(x²+2/3*x²)/(2/3*x²-4/9*x²-x²)=-15/7