1.
|a-1/2|+（b+1/3)²=0
|a-1/2|>=0
（b+1/3)²>=0
所以
a-1/2=0,b+1/3=0
a=1/2,b=-1/3
2.
4a²-2ab-b²
=4*(1/2)^2-2*1/2*(-1/3)-(1/3)^2
=1+1/3-1/9
=11/9