(10分) 已知数列{an}的前n项和Sn=10n-n2,(n∈N*). (1) 发布时间:2017-04-27 00:15 │ 来源:www.tikuol.com 题型:解答题 问题: (10分) 已知数列{an}的前n项和Sn=10n-n2,(n∈N*).(1)求a1和an;(2)记bn=|an|,求数列{bn}的前n项和.
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