2/5+2/45+2/117+2/221 简便计算过程,/是分数线

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2/5+2/45+2/117+2/221简便计算过程,/是分数线2/5+2/45+2/117+2/221简便计算过程,/是分数线2/5+2/45+2/117+2/221简便计算过程,/是分数线2/5=

2/5+2/45+2/117+2/221 简便计算过程,/是分数线
2/5+2/45+2/117+2/221 简便计算过程,/是分数线

2/5+2/45+2/117+2/221 简便计算过程,/是分数线
2/5=2/1X5=1/2(1-1/5)
2/45=2/5X9=1/2(1/5-1/9)
2/117=2/9X13=1/2(1/9-1/13)
2/221=2/13X17=1/2(1/13-1/17)
相加,上式=1/2(1-1/5+1/5-1/9+1/9-1/13+1/13-1/17)=1/2(1-1/17)=8/17