x^2+3xy-4y^2=0
(x+4y)(x-y)=0
x=-4y或x=y
所以(x+2y)/(2x-y)
=(-4y+2y)/(-8y-y)
=-2/(-9)
=2/9
或者=(y+2y)/(2y-y)
=3y/y
=3
所以原式=2/9或3