因为(a-2)²≥0√(b+1/2)≥0所以(a-2)²+√(b+1/2)≥0要使(a-2)²+√(b+1/2) ≤0只能(a-2)²+√(b+1/2) =0得a-2=0b+1/2=0解得a=2b=-1/2-2（3b²-2a²）+3（ab＋2b²-a²）=-6b²...