请大家算道题 很急！

绝对值的题目，关键是要搞清正负号。正数绝对值等于本身，负数绝对值等于相反数。

|1/2009-1/2008|=1/2008-1/2009
|1/2008-1/2007|=1/2007-1/2008
|1/2009-1/2007|=1/2007-1/2009

原式=（1/2008-1/2009）+（1/2007-1/2008）-（1/2007-1/2009）
=1/2008-1/2009+1/2007-1/2008-1/2007+1/2009
=0

化简原式=1/2008-1/2009+1/2007-1/2008-1/2007+1/2009=0

1/2009-1/2008的绝对值+1/2008-1/2007的绝对值-1/2009-1/2007的绝对值=(1/2008-1/2009)+(1/2007-1/2008)-(1/2007-1/2009)=0

[1/2009-1/2008]=1/2008-1/2009,同理；1/2008-1/2009+1/2007-1/2008-1/2007+1/2009=0

答案应该是0。
你将每个绝对值去掉就好算了！