设xy等于e的x+y次方确定了y=y（x）求dy/dx
问题描述：
设xy等于e的x+y次方确定了y=y（x）求dy/dx
答
xy=e^(x+y) 两边同时求导数
y+xy'=e^(x+y)(1+y')
y'[x-e^(x+y)]=e^(x+y)-y
y'=[e^(x+y)-y]/[x-e^(x+y)]