相关试题
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…的值等于( )
A.3n
B.3n-1
C.
D.
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若等比数列{an}的前n项和为Sn=3n+1+a,则常数a的值等于( )
A.
B.-1
C.
D.-3
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若一个等差数列的前n项和等于3n2+2n,其第k项是( )
A.3k2+2k
B.6k-1
C.5k+5
D.6k+2
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在数列{an}中,an+1=can(c为非零常数)且前n项和Sn=3n+k,则k等于( )
A.-1
B.1
C.0
D.2
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已知数列{an}前n项和,则an=( )
A.
B.3n-1
C.3•2n-1
D.2•3n-1
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数列{an}中,a1=1,an+1=an+4n-3,则数列{an}的通项公式为( )
A.2n2-n+1
B.2n2-3n+1
C.2n2-5n+4
D.2n2-3n+2
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已知等差数列{an}满足a2=3,a5=9,若数列{bn}满足,则{bn}的通项公式为( )
A.bn=3n+1
B.bn=2n+1
C.bn=3n+2
D.bn=2n+2
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若等比数列{an}的前n项和Sn=3n+r,则r=( )
A.0
B.-1
C.1
D.3
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等比数列的前n项和Sn=k•3n+1,则k的值为( )
A.-3
B.-1
C.1
D.3
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若{an}为递减数列,则{an}的通项公式可以为( )
A.an=2n+3
B.an=-n2+3n+1
C.
D.an=(-1)n