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=1/101+1/2又1/3又1/4=1+1/2又1/(13/4)=1+1...