已知正项数列{an},其前n项和Sn满足8Sn=an2+4an+3,且a2是a1和a7的等比中项.(Ⅰ)求数列{a n}的通项公式;(Ⅱ)设bn=log2an+34(n+1),求数列{b n}的前99项和.

问题描述:

已知正项数列{an},其前n项和Sn满足8Sn=an2+4an+3,且a2是a1和a7的等比中项.
(Ⅰ)求数列{

a  n
}的通项公式;
(Ⅱ)设bn=log2
an+3
4(n+1)
,求数列{
b  n
}
的前99项和.

(Ⅰ) 由8Sn=an2+4an+3  ①得8Sn-1=an-12+4an-1+3 (n≥2,n∈N)  ②由①-②得8an=(an-an-1)(an+an-1)+4an-4an-1,整理得(an-an-1-4)(an+an-1)=0(n≥2,n∈N),∵{an}为正项数列∴an+...