(1 减1/2)加(1/2减1/3)加(1/3减1/4)加(1/4减1/5).(1/2010 减1/2011) =1 - 1/2011 (注：中间相邻两项互相抵消,比如- 1/2 与1/2的和等于0,依次类推) =2000/2011