数列an是等差数列,首项不为0,求lim[Sn+S(n+1)]/[Sn-S(n+1)]
问题描述:
数列an是等差数列,首项不为0,求lim[Sn+S(n+1)]/[Sn-S(n+1)]
答
设等差数列{an}的前n项和Sn=An^2+Bn.(A+B不为0)
n是趋近于无穷吧:
(1)A=0即公差为0时,Sn=Bn.极限为-无穷(不存在).
(2)A不为0 时,Sn+S(n+1)是2次,Sn-S(n+1)是1次,极限不存在.