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2/1×3+2/3×5+2/5×7+···+2/19×21
人气:334 ℃ 时间:2020-05-23 12:20:54
解答
2/1×3+2/3×5+2/5×7+···+2/19×21
=(1/1-1/3)+(1/3-1/5)+(1/5-1/7)+···++(1/19-1/21)
=1-1/21
=20/21
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