数列{an}为等差数列,bn=ana(n-1)a(n-2)(n属于N+),数列{bn}的前n项和为Sn,3a5=8a12已知数列为等差数列且3a5=8a12>0 数列B满足bn=ana(n+1)a(n+2) bn的前n项和为Sn 当N 多大时Sn 取得最大值
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![数列{an}为等差数列,bn=ana(n-1)a(n-2)(n属于N+),数列{bn}的前n项和为Sn,3a5=8a12已知数列为等差数列且3a5=8a12>0 数列B满足bn=ana(n+1)a(n+2) bn的前n项和为Sn 当N 多大时Sn 取得最大值](/uploads/image/z/3991781-29-1.jpg?t=%E6%95%B0%E5%88%97%7Ban%7D%E4%B8%BA%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%2Cbn%3Dana%28n-1%29a%28n-2%29%28n%E5%B1%9E%E4%BA%8EN%2B%EF%BC%89%2C%E6%95%B0%E5%88%97%7Bbn%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2C3a5%3D8a12%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97%E4%B8%BA%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%E4%B8%943a5%3D8a12%3E0+%E6%95%B0%E5%88%97B%E6%BB%A1%E8%B6%B3bn%3Dana%28n%2B1%29a%28n%2B2%29+bn%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn+%E5%BD%93N+%E5%A4%9A%E5%A4%A7%E6%97%B6Sn+%E5%8F%96%E5%BE%97%E6%9C%80%E5%A4%A7%E5%80%BC)
数列{an}为等差数列,bn=ana(n-1)a(n-2)(n属于N+),数列{bn}的前n项和为Sn,3a5=8a12已知数列为等差数列且3a5=8a12>0 数列B满足bn=ana(n+1)a(n+2) bn的前n项和为Sn 当N 多大时Sn 取得最大值
数列{an}为等差数列,bn=ana(n-1)a(n-2)(n属于N+),数列{bn}的前n项和为Sn,3a5=8a12
已知数列为等差数列且3a5=8a12>0 数列B满足bn=ana(n+1)a(n+2) bn的前n项和为Sn 当N 多大时Sn 取得最大值
数列{an}为等差数列,bn=ana(n-1)a(n-2)(n属于N+),数列{bn}的前n项和为Sn,3a5=8a12已知数列为等差数列且3a5=8a12>0 数列B满足bn=ana(n+1)a(n+2) bn的前n项和为Sn 当N 多大时Sn 取得最大值
3a5=8a12=8(a5+7d)=8a5+56d
5a5+56d=0
5(a5+11d)+d=0
5a12+d=0
a12=-d/5>0 d0,第55、56、57项=0,第58项以后均
{an}是首相为1,公差为2的等差数列,bn=1/ana(n+1)求数列{bn}的前n项和
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