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](/uploads/image/z/10189604-20-4.jpg?t=2%2F5%2B2%2F45%2B2%2F117%2B2%2F221+%E7%AE%80%E4%BE%BF%E8%AE%A1%E7%AE%97%E8%BF%87%E7%A8%8B%2C%2F%E6%98%AF%E5%88%86%E6%95%B0%E7%BA%BF)
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