an=n+2 Sn=1/a1a2+1/a2a3+.+1/ana(n+1),求Sn

an=n+2 Sn=1/a1a2+1/a2a3+.+1/ana(n+1),求Sn 已知数列an的前n项和是Sn=n^2,则1/a1a2+1/a2a3+...+1/a(n-1)an=? 已知数列an的前n项和是Sn=n^2,则1/a1a2+1/a2a3+...+1/a(n-1)an=? 已知{an}是等比数列,an>0,sn=a1+a2+.an,Tn=1/a1+1/a2+.1/an,求证a1a2.an=(sn/Tn)^n/2 已知数列an满足a1=1,a（n+1）=an/{3（an）+1} Sn=a1a2+a2a3+.+an（an+1）,求Sn已知数列an满足a1=1,a（n+1）=an/{3（an）+1}Sn=a1a2+a2a3+......+an（an+1）,求Sn 等差数列an中,a(n+1)=2n+1,则Sn=(1/a1a2)+（1/a2a3）…（1/a99a100）= 已知数列AN满足an=1 且an=2A（n-1）+2的N次 1求a1a2 （2）证明数列AN/2n次是等差 （30）前N项和SN 已知{an} a1=-3.4Sn=(2n+3)an+1 (1)求an(2)求和1/a1a2+1/a2a3+```+1/an(an+1)为多少 已知数列前n项和为sn=1/3(an-1) 求a1a2 已知函数F（x）=2x/（x+2）数列An满足A1=4/3,A(n+1)=F(An)记Sn=A1A2+A2A3+.+AnA(n+1),求证Sn 求自然数a1a2.an,使得12×2 a1a2.an 1=21×1 a1a2.an 2 已知数列an的前n项和Sn=n^2+2n,求通项an 求和1/a1a2+1/a2a3+1/a3a4…1/anan+1 设数列{an}的前n项和为sn,且a1=1,sn=nan-2n(n-1)(n∈正整数)证明,证明1/a1a2+1/a2a3+.+1/an-an+1 已知数列an的前n项和Sn=2n^2+n,则lim[1/a1a2+1/a2a3+1/a3a4+...+1/anan+1]的值为 已知等差数列an前n项和为Sn,Sn=n^2,求和1/(a1a2)+1/(a2a3)+.+1/[(an-1an] (n≥2 )老师说,用裂项相消法,求完整过程, 已知数列｛an｝前n项和Sn=n^2+2n (1)求数列的通项公式an (2)设Tn=1/a1a2已知数列｛an｝前n项和Sn=n^2+2n(1)求数列的通项公式an(2)设Tn=1/a1a2+1/a2a3+…+1/(anan+1)求Tn 已知数列{an}是一个各项为正数的等比数列,Sn为它的前n项和,Bn=1/a1+1/a2+...+1/an,Pn=a1a2...an求证:Pn=(Sn/Bn)^(n/2) 已知数列{An}的前n项和为Sn,A1=A2=1,bn=nSn+（n+2)An,数列{bn}是公差为d的等差数列,证（A1A2.An)(S1.Sn)