42*(1/8+1/24+1/48+1/86+1/120+1/168) 简便方法

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42*(1/8+1/24+1/48+1/86+1/120+1/168) 简便方法
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42*(1/8+1/24+1/48+1/86+1/120+1/168) 简便方法
42*(1/8+1/24+1/48+1/86+1/120+1/168) 简便方法

42*(1/8+1/24+1/48+1/86+1/120+1/168) 简便方法
42*(1/8+1/24+1/48+1/80+1/120+1/168)
=42*1/2*(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12+1/12-1/14)
=21*(1/2-1/14)
=21*3/7
=9