2005 2005 2005 2005 2005

问题描述:

2005 2005 2005 2005 2005
--- +___ + ___+---+.+---------=(
1X2 2X3 3X4 4X5 2004X2005

原式=2005×(1-1/2+1/2-1/3+1/3-1/4.+1/2004-1/2005)
=2005×(1-1/2005)
=2004