赞 xiaohh1234 幼苗
共回答了11个问题采纳率：81.8% 举报
2/11*13+2/13*15+2/15*17+2/17*19+2/19*21
=1/11-1/13+1/13-1/15+1/15-1/17=1/17-1/19+1/19-1/21
=1/11-1/21
=10/231
=1/11-1/13+1/13-1/15+1/15-1/17=1/17-1/19+1/19-1/21
=1/11-1/21
=10/231
1年前
10
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