海不扬波波
幼苗
共回答了18个问题采纳率:94.4% 举报
1/(1×3)=1/2(1-1/3)
1/(2×4)=1/2(1/2-1/4)
1/(3×5)=1/2(1/3-1/5)
…
1/(9×11)=1/2(1/9-1/11)
以上九个等式相加得:
1/(1×3)+1/(2×4)+1/(3×5)+…+1/(9×11)
=1/2(1-1/3)+1/2(1/2-1/4)+1/2(1/3-1/5)+…+1/2(1/9-1/11)
=1/2(1+1/2-1/10-1/11)
=127/220
1年前
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