计算1/2加1/6加1/12加1/20加1/30加1/42加1/56加1/72加1/90

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计算1/2加1/6加1/12加1/20加1/30加1/42加1/56加1/72加1/90

计算1/2加1/6加1/12加1/20加1/30加1/42加1/56加1/72加1/90
计算1/2加1/6加1/12加1/20加1/30加1/42加1/56加1/72加1/90

计算1/2加1/6加1/12加1/20加1/30加1/42加1/56加1/72加1/90
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/10
=9/10

0.9

解原式=1-1/2十1/2-1/3十1/3-1/4……-1/9十1/9-1/10
=1-1/10
=9/10