caodongbeiren
幼苗
共回答了22个问题采纳率:90.9% 举报
此类题最常见的解法是拆项法来解
因为1/n(n+1)=1/n-1/(n+1)
所以
Sn=1/1X2+1/2X3+1/3X4+…+1/n(n+1)
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+…+(1/n-1/(n+1))
=1-1/(n+1)
=n/(n+1)
求1/1X3+1/3X5+1/5X7,…1/(2n-1)(2n+1)也是用拆项法来解
利用1/(2n-1)(2n+1)=(1/2)[1/(2n-1)-1/(2n+1)]
1年前
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