mn互为相反数 =>m+n=0 ; pq互为倒数=> pq=1 ; a的绝对值是2 => a=2 or -2 ;a^2=4
=> (m+n)/2012*a*p*q =0/2012a =0
=> - (1/4) a^2 = -(1/4)*4 =-1