1 - 1／2 - 1／6- 1／12 - 1／20 - 1／30 - 1／42 - 1／56 - 1／72 - 1／90
=1-(1/1*2+1/2*3+1/3*4+...+1/9*10)
=1-(1-1/2+1/2-1/3+1/3-1/4+...+1/9-1/10)
=1-(1-1/10)
=1-9/10
=1/10
1+1/2又1/3又1/4
=1+1/2又1/(13/4)
=1+1/(15/2)
=1+2/15
=1又2/15
1.计算：1 - 1／2 - 1／6- 1／12 - 1／20 - 1／30 - 1／42 - 1／56 - 1／72
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