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1/1乘2乘3+1/2乘3乘4+1/3乘4乘5
人气:464 ℃ 时间:2020-06-17 22:53:18
解答
=1/2×(1/1×2-1/2×3+1/2×3-1/3×4+1/3×4-1/4×5)
=1/2×(1/1×2-1/4×5)
=9/40
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