m、n互为相反数——>m+n=0
p、q互为倒数——>pq=1
a的绝对值为2——>a=2或-2
(m+n)/2008*a-2009pq+(1/4)a²
=0/2008*a-2009*1+(1/4)*4
=0-2009+1
=-2008