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已知等差数列{an}是递增数列,且满足a4•a7=27,a2+a9=12.(1)求数列{a...
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已知等差数列{a
n}是递增数列,且满足a
4•a
7=27,a
2+a
9=12.
(1)求数列{a
n}的通项公式;
(2)令
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)
n项和S
n.
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