赞 jackyluolz 幼苗
共回答了22个问题采纳率：81.8% 举报
1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)+1/(7×8)+1/(8×9)
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/3-1/9
=2/9
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/3-1/9
=2/9
1年前 追问
7
分数裂项 1/(3×4)=1/3-1/4 1/(4×5)=1/4-1/5 ...... 1/(8×9)=1/8-1/9 中间互相抵消,最后就剩下1/3-1/9=2/9
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你能帮帮他们吗