y=1+xe^yy'= e^y + (xe^y)y'(1-xe^y)y' = e^yy' =e^y/(1-xe^y)y'' =[e^y/(1-xe^y)]y' - [ e^y/(1-xe^y)^2] .[ -e^y - xe^y.y']=[e^y/(1-xe^y)].[e^y/(1-xe^y)] - [ e^y/(1-xe^y)^2] .{ -e^y - xe^y.[e^y/(1-xe^y)] }=e^(2y)/(1-xe^y)^2 - [ e^y/(1-xe^y)^2] .[ -e^y /(1-xe^y)] =e^(2y)/(1-xe^y)^2 + e^(2y)/(1-xe^y)^3
两边求导y'=e^y+y'xe^yy'(1-xe^y)=e^yy''(1-xe^y)-y'(e^y+y'xe^y)=y'e^yy''(1-xe^y)-y'y'=y'e^yy''(1-xe^y)-[e^y/(1-xe^y)]^2=e^2y/(1-xe^y)y''=e^2y/(1-xe^y)^3+e^2y/(1-xe^y)^2