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求和Sn=1/(1*4)+1/(2*7)+.+1/n*(3n+1)
人气:477 ℃ 时间:2020-02-05 23:46:35
解答
Sn=3/3{1/(1*4)+1/(2*7)+……+1/[n*(3n+1)]}
=3{1/(3*4)+1/(6*7)+……+1/[3n*(3n+1)]}
=3{1/3-1/4+1/6-1/7+1/9-1/10+……+1/3n-1/(3n+1)}
好像无解.是不是题错了?
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