（a-3/2)的平方+（b+1/4)=0 即a-3/2=0,b+1/4=0 所以a＝3/2,b＝-1/4 c+d＝0 故2a+b-c/2-d/2 =[(2a+b)-(c+d)]/2 =(3-1/4-0)/2 =11/4/2 =11/8