希望对你有帮助
(1)2an =Sn+2n=1a1=22an =Sn+22[Sn-S(n-1)] =Sn+2Sn +2= 2[S(n-1)+2](Sn +2)/[S(n-1)+2] =2(Sn +2)/(S1 +2)=2^(n-1)Sn +2 =2^(n+1)Sn = -2+ 2^(n+1)an =Sn-S(n-1) = 2^n
