设sn是等差数列{an}的前几项和,若s7=35,求a4
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设sn是等差数列{an}的前几项和,若s7=35,求a4
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设Sn是等差数列{an}的前n项和,已知S8=108,Sn=630,S(n-8)=234,求n.
设Sn是等差数列{an}的前n项和,已知S8=108,Sn=630,S(n-8)=234,求n.
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