（a-3/2）的平方+|b+1/4|=0
a-3/2=0 b+1/4=0
a=3/2 b=-1/4
c与d为相反数
c+d=0
2a+b-c/3-d/3
=2*(3/2)-1/4-1/3(c+d)
=3-1/4+0
=11/4