|1/2 -1|+|1/3-1/2|+|1/4-1/3|+.+|1/2009-1/2008|
=1-1/2+1/2-1/3+1/3-1/4+.1/2008-1/2009
=1-1/2009
=2008/2009
每个绝对值里的数都小于零,去掉绝对值时变号
不懂得继续问哦^_^