∵（a＋2）²+丨3b-1丨=0
∴（a＋2）²≥0,丨3b-1丨≥0
∴a=-2,b=1/3
∵3a²b-[3ab²-6（ab-½a²b）+4ab]-2ab
=3a²b-[3ab²-6ab+3a²b+4ab]-2ab
=3a²b-3ab²+6ab-3a²b-4ab-2ab
=-3ab²
把a=-2,b=1/3代入得
=-3·（-2)·(1/3)²
=2/3