已知x平方+3xy-4y2=0(y不等于0),求x-y/x+y的值为?

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已知x平方+3xy-4y2=0(y不等于0),求x-y/x+y的值为?

x^2+3xy-4y^2=0
(x-y)(x+4y)=0
x=y或x=-4y.
∴(x-y)/(x+y)=(y-y)/(y+y)=0
或(x-y)/(x+y)=(-4y-y)/(-4y+y)=5/3.