已知等差数列{an},a3=7.a5+a7=26.{an}的前n项和为Sn.1.求a4及Sn.
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已知等差数列{an},a3=7.a5+a7=26.{an}的前n项和为Sn.1.求a4及Sn.
已知等差数列{an},a3=7.a5+a7=26.{an}的前n项和为Sn.1.求a4及Sn.
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已知等差数列{an}满足:a3=7,a5+a7=26,{an}的前n项和为Sn.求an及Sn.
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已知等差数列{an}满足:a3=7,a5+a7=26.{an}的前n项和为Sn.(1)求an及Sn; (2)令bn=1/
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已知数列{an}是等差数列,它的前n项和为Sn.a1+a2+a3=4,a3+a4+a5=10.求SN