(1/2*4)+(1/4*6)+(1/6*8)+.+(1/2006*2008)
=1/2(1/2-1/4+1/4-1/6+1/6-1/8+.+1/2006-1/2008)
=1/2(1/2-1/2008)
=1003/4016
盐中的不,我们老师刚讲过.