等差数列前n项和an=(1/n+1)+(2/n+1)+...+(n/n+1).又bn=2/an×a(n-1),求bn的前n项和.

为什么等差数列中an=A(2n-1)?An为等差数列前n项和. 等差数列{an}前n项和为sn,求证S2n-1=(2n-1)an 等差数列前n项和为Sn=1/2(An+1/An),求通项An 等差数列{an}前n项和为Sn,求证S 2n-1项=（2n-1）an 等差数列an=2n-1,求数列{1/an*a n+1}的前n项和Sn 等差数列an前n项和为Sn,求证S（2n-1）=（2n-1）an 已知数列{an}的前N项和sn=n^2+n+1,an是否为等差数列? 已知一等差数列{an}的前n项和Sn=n^2-3n+1,求an 等差数列前n项和为Sn,求证:S2n-1=(2n-1)an 等差数列an的前n项和Sn=(n+1)²+λ,则λ= 等差数列{an},{bn}的前n项和分别为An,Bn,切An/Bn=2n/3n+1,求lim(n→∞)an/bn 已知数列an前n项和sn=n平方＋1an前五项?是否等差数列?an通向公式 数列an ,a1=1,前n项和为Sn ,正整数n对应的n an Sn 成等差数列.1.证明{Sn+n+2}成等比数列,2.求{n+2/n(n+1)(1+an)}前n项和 (1)已知数列an的前n项和为sn满足sn=an²+bn,求证an是等差数列(2)已知等差数列an的前n项和为sn,求证数列sn/n也成等差数列 等差数列{an}前n项和Sn=-n²+n,求等差数列的首项 已知等差数列｛an｝的前n项和为Sn=n^2+2n,(n∈+N),（1）求通项an （2）记bn=an×3^n,求数列｛bn｝的前n项和Tn. 等差数列{an}的前n项和为An,等差数列{bn}的前n项和为Bn若Bn/An=n/3n+1 1.求a5/b5 2 an/bn 等差数列an的前n项和为Sn=n^2+4n-1,则通项公式为?