∵（a+b)²+|2b-1|=0
∴(a+b)²=0,|2b-1|=0
a+b=0,2b-1=0
解得：a=-½,b=½
ab-[2ab-3(ab-1)]
=ab-(2ab-3ab+3)
=ab-(-ab+3)
=ab+ab-3
=2ab-3
当a=-½,b=½时,
原式=2×(-½)×½-3
=-½-3
=-7/2