※ 引述《anger50322 (江)》之銘言：
: 欸欸用。我(x+y)/(x-y)=1/y,求dy/dx=?
: 答案是 (1-y)/(x+2y+1)
: 算不出這個答案
: http://i.imgur.com/TCtpjgh.jpg附上算式,請教各位
不一定要直接硬算，可以稍微先化簡
(x+y)/(x-y) = 1/y => 1 + 2y/(x-y) = 1/y
=> 1 = (x-y-2y^2)/(y*(x-y))
=> xy = x - y - y^2
所以， y + x dy/dx = 1 - dy/dx - 2y*dy/dx
整理一下得到， dy/dx = (1-y)/(x+2y+1)