已知3x^2+xy-2y^2=0,

已知3x^2+xy-2y^2=0,
已知3x^2+xy-2y^2=0,

已知3x^2+xy-2y^2=0,
原式可变形为（x+y）（3x-2y）=0,所以x=-y或3x=2y
由第二个分式可以知道x不等于±y,所以x=2y/3
然后把代数式化简以后再代入,这个自己动手

x^2+2xy-3y^2=(x+3y)(x-y);
x^-9y^2=(x-3y)(x+3y);
该式=（x-y）/(x-3y)
3x^2+xy-2y^2=(x+y)(3x-2y)=0,得到x=-y或者3x=2y,带入即可

3x^2+xy-2y^2=（3x-2y)(x+y)=0
得x=-y或x=2y/3
当x=-y时，[（x+y)/(x-y)]+[(4xy)/(y^2-x^2)]无意义
当x=2y/3时，[（x+y)/(x-y)]+[(4xy)/(y^2-x^2)]=-5+24/5=-1/5
(x^2+2xy-3y^2)/(x^2-9y^2)=(4/9+4/3-3)/(4/9-9)=1/7
[（x+y)/(x-y)]+[(4xy)/(y^2-x^2)]÷(x^2+2xy-3y^2)/(x^2-9y^2)
=(-1/5)÷(1/7)
=-7/5