观察:1/2×3=1/2-1/3 1/3×4=1/3-1/4 1/4×5=1/4-1/5 计算:1/6+1/12+1/20+1/30+…1/2005×2006

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观察:1/2×3=1/2-1/3 1/3×4=1/3-1/4 1/4×5=1/4-1/5 计算:1/6+1/12+1/20+1/30+…1/2005×2006

1/6+1/12+1/20+1/30+…1/2005×2006
=1/2-1/3+1/3-1/4+1/4-1/5………………+1/2005-1/2006(中间的全部抵消)
=1/2-1/2006
=1002/2006
=501/1003

1/6+1/12+1/20+1/30+…1/2005×2006
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+…+1/2005-1/2006
=1/2--1/2006
=1002/2006
=501/1003

1/2-1/2006