1/3*1+1/3*5+1/5*7+----1/17*19+1/19*21
=1-1/3+1/3-1/5+1/5-1/7+,+1/17-1/19+1/19-1/21
=1-1/21
=20/21
1/3*1+1/3*5+1/5*7+----1/17*19+1/19*21=
1/3*1+1/3*5+1/5*7+----1/17*19+1/19*21=
数学人气：348 ℃时间：2019-12-08 03:42:10
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