当|a+2|+(x-3)^2=0时
a+2=0 x-3=0
a=-2 x=3
1/3(-3ax^2-ax+3)-(-ax^2-1/2ax-1)
=1/3(-3*-2*3^2+2x3+3)-(2x3^2-1/2x-2*3-1)
=1/3(54+6+3)-(18+3-1)
=21-20
=1