已知等差数列前三项为a,4,3a,前n项和为Sn,Sk=2550.求1/S1+1/S2+……+1/Sn
1个回答
Si=i(i+1) 1/Si=1/i -1/(i+1) 所以原式=1-1/(N+1)
记得采纳啊
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