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数学
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1/1×3 + 1/3×5 + 1/5×7 +.+ 1/19×21=
说明一下我不止是要答案,还要这样做的理由,
人气:130 ℃ 时间:2020-05-17 04:52:37
解答
1/1×3 + 1/3×5 + 1/5×7 +.+ 1/19×21
=(1-1/3)÷2+(1/3-1/5)÷2+(1/5-1/7)÷2+……+(1/19-1/21)÷2
=(1-1/3+1/3-1/5+1/5-……-1/19+1/19-1/21)÷2
=(1-1/21)÷2
=20/21÷2
=10/21
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