二个式子都是一样的,y'=dy/dx
至于第二步为啥不一样,这个就是你的问题了
两种方法都正确,你第一种计算错误
两边同时求微分
2dy-dx=(dx-dy)ln(x-y)+(x-y)(dx-dy)/(x-y)
2dy-dx=ln(x-y)dx-ln(x-y)dy+dx-dy
dy=[2+ln(x-y)]dx/[3+ln(x-y)]
method 1
2y-x=(x-y)ln(x-y)
2dy-dx = [(x-y)/(x-y)]( dx - dy) + (dx-dy).ln(x-y)
= (dx -dy) [1 -ln(x-y) ]
[3+ln(x-y) ]dy = [2-ln(x-y)] dx
dy = [2-ln(x-y)] dx /[3+ln(x-y) ]
这样才对