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╱/●.墨· 在墨后面加个字 加什么字好(

1- 1/2 -1/6 -1/12 -1/20 -1/30 -1/42
=1- [1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)]
=1-(1- 1/2 +1/2 -1/3 +1/3 -1/4 +1/4 -1/5+ 1/5- 1/6+ 1/6- 1/7)
=1-(1- 1/7)
=1-1+1/7
=1/7
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2024-06-01 19:59:24
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