a^2+b^2+2a+4b+5=0
(a+1)^2+(b+2)^2=0
(a+1)^2=0
a+1=0
a=-1
(b+2)^2=0
b+2=0
b=-2
[（a+1/2b)+(a-1/2b)^2]（2a^2-1/2b^2）
=[(-1-2*1/2)+(-1-2*1/2)^2][2(-1)^2-1/2(-2)^2]
=[-2+4][2-2]
=0