简单分析一下，答案如图所示
y+e^(x+y)=2x,两边求导得y'+e^(x+y)*(1+y')=2,整理得[1+e^(x+y)]y'=2-e^(x+y),∴y'=[2-e^(x+y)]/[1+e^(x+y)]=-1+3/[1+e^(x+y)],再求导得y''=-3/[1+e^(x+y)]^2*e^(x+y)*(1+y')=-9e^(x+y)/[1+e^(x+y)]^3.
