1.设等差数列{an}满足:设等差数列{an}满足:[sin^2(a3)-cos^2(a3)+cos^2(a3)*cos^2(a6)-sin^2(a3)*sin^2(a6)]/sin(a4+a5)=1,公差d∈（-1,0）.若当且仅当n=9时,数列{an}的前n项和Sn取得最大值,则首项a1的取值范围是（）A.

设等差数列{an}满足a3=5 a10=-9 求{an}的通项公式 设数列an是等差数列,a1 设数列an是等差数列,a1 设数列{an}满足an=2an-1+n 若{an}是等差数列,求{an}通项公式 设等差数列{an}的前n项和为Sn,且满足S15>0,S16 已知递增的等差数列{an},满足a1=1,且a1,a2,a5成等比数列1.求等差数列{an},的通项an2.设bn=an+2^an,求数列｛bn｝的前n项Sn 设数列an,bn满足:bn=(a1+a2+a3+a4+...+an)/n,若bn是等差数列,求证an也是等差数列 设等比数列｛An｝中,满足等差数列｛Bk｝各项均为正整数,证明数列｛Abk｝为等比数列 .设等比数列｛An｝中,满足等差数列｛Bk｝各项均为正整数,证明数列 如图 为等比数列 .若等比数列｛An｝ 设a,b是正整数,{an}是首项是a,公差为b的等差数列,{bn}是首项是b,公差为a的等差数列且满足a1 关于数列、等差数列的题目设数列an满足an+1=an-2且a1=241）判断an是什么数列2）若an 已知数列{an},{bn}满足a1=2,2an=1+2an*an+1,设{bn}=an-1求数列{1n}为等差数列急！！！ 设{an}是等差数列,a3=12,S12>0,S13 设{An}是等差数列,a3=12,S12>0,S13 设{an}是等差数列,{bn}是等比数列,且0 设等差数列{an}满足3a8=5a13且a1>0,求Sn的最大值是 n取什么? 设等差数列满足an=2an-1+n(n=2,3,.).求通项公式设等差数列满足an=2an-1+n(n=2,3,.)（1）若an是等差数列,求an的通项公式（2）an是否可能为等比数列?若可能,求出此数列通项公式,若不可能,说明理由.过 设数列{an}满足：a1+a2/2+a3/3+a4/4……+an/n=An+B,其中A、B为常数.数列{an}是否为等差数列? 设数列an的前n项和为Sn,满足an+sn=An^2+Bn+1(A不等于0)an为等差数列,求(B-1)/A