{an}是等差数列且an不等于0 （n=1,2,...）求证：级数1/an发散

已知数列{an}是等差数列,且bn=an+a(n-1),求证bn也是等差数列 已知{an}是等差数列,公差d不等于0,且a1 a3 a13成等比数列,sn是{an}的前n项和,（1）求证s1 s2 已知数列{an}得前n项和为sn=an^2+bn(a,b为常数且a不等于0)求证数列{an}是等差数列 已知数列{an}中a1=-1且(n+1)an,(n+2)an+1(是下标)成等差数列,设bn=(n+1)an-n+2求证 已知数列an是等差数列,且bn=an+a（n+1）.求证数列bn是等差数列. 已知数列{An}是等差数列,且Bn=An+A（n+1）.求证数列{Bn}是等差数列 已知数列{An}满足A1=1,An+1=2An+2^n.求证数列An/2是等差数列 已知数列{an}满足an+an+1=2n+1（n∈N*），求证：数列{an}为等差数列的充要条件是a1=1． {an}为等差数列,an不等于0,d为公差,求证:1/(a1a2)+1/(a2a3)+...+1/(an-1*an)=( 已知f(x)=3x/(x+3),数列{an}满足an=f(an-1) (n>1,a1≠0）求证①{1/an}是等差数列 数列{an}前n项和Sn=npa[n](n是正整数),且a1不等于a2,(1)求p的值(2)证明{an}为等差数列 各项均为正数的数列{an}的前n项和为S,且sn=1\8(an+2)².求证数列{an}是等差数列