1×1/2=1-1/2,1/2×1/3=1/2-1/3,1/3×1/4=1/3-1/4......
所以原式化为1-1/2+1/2-1/3+1/3-1/4+1/4-1/5.....+1/2004-1/2005+1/2005-1/2006=1-1/2006=2005/2006
原式=1-1/2+1/2-1/3+1/3-1/4+......+1/2005-1/2006
=2005/2006
=1/2+(1/2-1/3)+(1/3-1/4)+...+(1/2005-1/2006)
=1-1/2006
=2005/2006
=1-1/2+1/2-1/3+1/3-1/4......+1/2005-1/2006
=1-1/2006
=2005/2006