y=lnx/xy'=(1-lnx)/x^2=1/x^2-lnx/x^2y"=-2/x^3-(1-2lnx)/x^3=-3/x^3+2lnx/x^3记y(n)=(-1)^(n+1)*[ an- n!lnx]/x^(n+1)有y(n+1)=(-1)^n*an (n+1)/x^(n+2)+(-1)^n* n![1- (n+1)lnx]/x^(n+2) a(n+1)=(n+1)an+n!a1=1, a2=3,a3=11,a4=50,a5=274....