(x-2y)dx=2ydy
(x-2y)/2y=dy/dx
x/(2y)-1=y'
令y=px
y'=p'x+p
上式化为
1/(2p)-1=p'x+p
p'x=1/(2p)-p-1
dp/[1/(2p)-p-1]=dx/x
-2pdp/(2p^2+2p-1)=dx/x
好象不对啊