当n=1时,a1+2S1=1 即：a1+2a1=1 a1=1/3由an+2Sn=1可得：a(n-1)+2S(n-1)=1a(n-1)+2(Sn-an)=1则：2Sn=1+2an-a(n-1)代入an+2Sn=1中得：an+1+2an-a(n-1)=13an=a(n-1)an/a(n-1)=1/3则{an}是以1/3为首项,公比为1/3的等比数...
