dy/dx=1+7/(x-y-2)
令x-y-2=u 1-y'=u'
1-u'=1+7/u u'=-7/u
u^2=-14x+C
或：(x-y-2)^2=-14x+C令x-y-2=u 怎么得到1-y'=u'？？？谢谢两边对x求导额，好吧，我懂了，谢谢