已知数列{An}是一个首项为1,公差为2/3的等差数列,Bn=[(-1)^(n-1)]*An*A(n+1),\x0d设数列{Bn}的前n项和为Sn,求Sn.\x0d答案是:\x0dSn=-2n^2/9-2n/3(n为偶数)\x0d 或=2n^2/9+2n/3+7/9(n为奇数)\x0d这是怎么做出来的?\x0d
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/08 16:13:40
![已知数列{An}是一个首项为1,公差为2/3的等差数列,Bn=[(-1)^(n-1)]*An*A(n+1),\x0d设数列{Bn}的前n项和为Sn,求Sn.\x0d答案是:\x0dSn=-2n^2/9-2n/3(n为偶数)\x0d 或=2n^2/9+2n/3+7/9(n为奇数)\x0d这是怎么做出来的?\x0d](/uploads/image/z/2782331-35-1.jpg?t=%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97%7BAn%7D%E6%98%AF%E4%B8%80%E4%B8%AA%E9%A6%96%E9%A1%B9%E4%B8%BA1%2C%E5%85%AC%E5%B7%AE%E4%B8%BA2%2F3%E7%9A%84%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%2CBn%3D%5B%28-1%29%5E%28n-1%29%5D%2AAn%2AA%28n%2B1%29%2C%5Cx0d%E8%AE%BE%E6%95%B0%E5%88%97%7BBn%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2C%E6%B1%82Sn.%5Cx0d%E7%AD%94%E6%A1%88%E6%98%AF%EF%BC%9A%5Cx0dSn%3D-2n%5E2%2F9-2n%2F3%28n%E4%B8%BA%E5%81%B6%E6%95%B0%29%5Cx0d+%E6%88%96%3D2n%5E2%2F9%2B2n%2F3%2B7%2F9%28n%E4%B8%BA%E5%A5%87%E6%95%B0%29%5Cx0d%E8%BF%99%E6%98%AF%E6%80%8E%E4%B9%88%E5%81%9A%E5%87%BA%E6%9D%A5%E7%9A%84%3F%5Cx0d)
xSkOP+ IK=m֬>"LhH"(x*A\bigv_=mG&1&|CO{'+4LCJ(V(.taa:9o5/"gĽN Fv}B潎"g q*8rM1uԙrӸ\=4W?+n[ۄ&bnyw=m$
zuO0GL#;:Zqv"+dG CYO"aYSNtOyt4]6-)2D$RS78^AeɒlɊd!0,
Y1M##ٶxTV"ɤdUeI
KESQe=Oel rLް+ cwjnlgS˲ƭxA<ӷyv_W:)tmP뽣xZs^