1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算

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1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算
=1/1* 1/2+1/2*1/3+1/3*1/4+...+1/9*1/10
=1/1-1/2+1/2-1/3+1/3-1/4+...+1/9-1/10
=1/1-1/10
=9/10