1/5*8+1/8*11+1/11*14+1/14*17+1/17*20=1/20的计算过程

1/5*8+1/8*11+1/11*14+1/14*17+1/17*20=1/20的计算过程
1/5*8+1/8*11+1/11*14+1/14*17+1/17*20=1/20的计算过程

1/5*8+1/8*11+1/11*14+1/14*17+1/17*20=1/20的计算过程
1/(5×8)+1/(8×11)+1/(11×14)+1/(14×17)+1/(17×20)
=(1/3)(1/5-1/8+1/8-1/11+1/11-1/14+1/14-1/17+1/17-1/20)
=(1/3)(1/5-1/20)
=(1/3)(3/20)
=1/20

1/5*8+1/8*11+1/11*14+1/14*17+1/17*20
=1/3X（1/5-1/8+1/8-1/11+……1/17-1/20）
=1/3X（1/5-1/20）
=1/3X3/20
=1/20

1/5*8+1/8*11+1/11*14+1/14*17+1/17*20
＝1/3(1/5-1/8)+1/3(1/8-1/11)+1/3(1/11-1/14)+1/3(1/14-1/17)+1/3(1/17-1/20)
＝1/3(1/5-1/8+1/8-1/11+1/11-1/14+1/14-1/17+1/17-1/20)
＝1/3(1/5-1/20)
＝1/3*(3/20)
＝20
（用的拆项法）