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等差数列{an}的前n项和为Sn,若a2+a7+a9=15,则S11的值为A.B.50C....
试题详情
等差数列{a
n}的前n项和为S
n,若a
2+a
7+a
9=15,则S
11的值为( )
A.
B.50
C.55
D.110
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