x2-2xy+y2-4y2=0
(x-y)2-4y2=0
x-y=+2y或-2y
当x-y=+2y
x=3y
所以(2x+3y)/2y=(2*3x+3y)/2y=9/2
当x-y=-2y
x=-y
所以(2x+3y)/2y=[2*(-y)+3y]/2y=1/2