已知正项数列{an},{bn}满足a1=3,a2=6,{bn}是等差数列,且对任意正整数n,都有bn,,bn+...
问题详情:
已知正项数列{an},{bn}满足a1=3,a2=6,{bn}是等差数列,且对任意正整数n,都有bn,,bn+1成等比数列.
(1)求数列{bn}的通项公式;
(2)设Sn=++…+,试比较2Sn与2-的大小.
【回答】
解:(1)∵对任意正整数n,都有bn,,bn+1成等比数列,且{an},{bn}都为正项数列,
∴an=bnbn+1(n∈N*).
可得a1=b1b2=3,a2=b2b3=6,
又{bn}是等差数列,∴b1+b3=2b2,
解得b1=,b2=.∴bn=(n+1).
知识点:数列
题型:解答题