1,数列{an}的前n项和sn=n²+2n+5,则a6+a7+a8=?2,已知数列{an},a1=2,an+1=an+3n+2,则an=?3,已知等差数列{an}的前n项和为sn,若向量OB=a1OA+a2007OC,且A,B,C,三点共线(O是该直线外一点),则S2007等于?4,已
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![1,数列{an}的前n项和sn=n²+2n+5,则a6+a7+a8=?2,已知数列{an},a1=2,an+1=an+3n+2,则an=?3,已知等差数列{an}的前n项和为sn,若向量OB=a1OA+a2007OC,且A,B,C,三点共线(O是该直线外一点),则S2007等于?4,已](/uploads/image/z/1159961-41-1.jpg?t=1%2C%E6%95%B0%E5%88%97%EF%BD%9Ban%EF%BD%9D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8Csn%3Dn%26sup2%3B%2B2n%2B5%2C%E5%88%99a6%2Ba7%2Ba8%3D%3F2%2C%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97%EF%BD%9Ban%EF%BD%9D%2Ca1%3D2%2Can%2B1%3Dan%2B3n%2B2%2C%E5%88%99an%3D%3F3%2C%E5%B7%B2%E7%9F%A5%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%EF%BD%9Ban%EF%BD%9D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BAsn%2C%E8%8B%A5%E5%90%91%E9%87%8FOB%3Da1OA%2Ba2007OC%2C%E4%B8%94A%2CB%2CC%2C%E4%B8%89%E7%82%B9%E5%85%B1%E7%BA%BF%EF%BC%88O%E6%98%AF%E8%AF%A5%E7%9B%B4%E7%BA%BF%E5%A4%96%E4%B8%80%E7%82%B9%EF%BC%89%2C%E5%88%99S2007%E7%AD%89%E4%BA%8E%3F4%2C%E5%B7%B2)
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