|1/3-1/2|+|1/4-1/3|+|1/5-1/4+......+|1/2007-1/2006|+
|1/2008-1/2007|+|1/2009-1/2008|
=1/2-1/3+1/3-1/4+1/4-1/5+......+1/2007-1/2008+1/2008-1/2009
=1/2-1/2009
=2007/4018
这个题重点在于把绝对值符号拆掉,一个数的绝对值一定是正数,所以
|1/3-1/2|可以变成1/2-1/3,依次类推就得到答案了