S1= -39,an=Sn-Sn-1=2n-11(n>1)
bn=nan=2n^2-11n,设第k项最小
所以:bk
若数列{an}的前n项和Sn=n^2-10n-30,则数列{n*an}的最小项是第几项
若数列{an}的前n项和Sn=n^2-10n-30,则数列{n*an}的最小项是第几项
数学人气:580 ℃时间:2020-01-30 04:07:41
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