摘要:记数列{an}的前n项和为Sn.且Sn=2n(n-1).则该数列是 ( ) A.公比为2的等比数列 B.公比为的等比数列 C.公差为2的等差数列 D.公差为4的等差数列 解析:由条件可得n≥2时.an=Sn-Sn-1=2n(n-1)-2(n-1)(n-2)=4(n-1).当n=1时.a1=S1=0.代入适合.故an=4(n-1).故数列{an}表示公差为4的等差数列. 答案:D
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记数列{an}的前n项和为Sn,且an=6n2+2n-1,则Sn=
[ ]
A.
n2(2n-1)
B.
n·(6n2+2n-1)
C.
2n(n2+2n-1)
D.
n·(2n2+4n+1)?
设数列{an}的前n项和为Sn,且Sn=(1+λ)-λan,其中λ≠-1,0;
(1)证明:数列{an}是等比数列.
(2)设数列{an}的公比q=f(λ),数列{bn}满足
,bn=f(bn-1)(n∈N*,n≥2)求数列{bn}的通项公式;
(3)记λ=1,记
,求数列{cn}的前n项和为Tn
数列{an}的前n项和为Sn,且a1=1,3tSn-(2t+3)Sn-1=3t,其中t>0,n∈N*,n≥2.
(1)求证:数列{an}是等比数列;
(2)设数列{an}的公比为f(t),数列{bn}满足b1=1,bn=
(n≥2),求{bn}的通项公式;
(3)记Tn=b1b2-b2b3+b3b4-b4b5+…+b2n-1b2n-b2n+1,求证:Tn≤
.