等差数列{an}的各项均为正整数,a1=3,前n项和为Sn,等比数列{bn}中,b1=1,且b2S2=64,{ban}是公比为64的等比数列.(1)求{an}与{bn};(2)证明:1/S1+1/S2+…+1/Sn<3/4.
等差数列{an}的各项均为正整数,a1=3,前n项和为Sn,等比数列{bn}中,b1=1,且b2S2=64,{ban}是公比为64的等比数列.
(1)求{an}与{bn};
(2)证明:
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+…+
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(1)求{an}与{bn};
(2)证明:
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S1 |
1 |
S2 |
1 |
Sn |
3 |
4 |
数学人气:174 ℃时间:2019-08-21 03:45:53
优质解答
(1)设{an}的公差为d,{bn}的公比为q,则d为正整数,an=3+(n-1)d,bn=qn-1依题意有ban+1ban=q2+ndq2+(n-1)d=qd=64,且S2b2=(6+d)q=64,①由(6+d)q=64知q为正有理数,故d为6的因子1,2,3,6之一,解①得d=2,...
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