由|a-2|+(b+1)的平方=0
得：a-2=0,则a=2
b+1=0,则b=-1
3a²b+ab²-(3a²b-5ab)+ab²-4ab+1/2a²b
=3a²b+ab²-3a²b+5ab+ab²-4ab+1/2a²b
=2ab²+ab+1/2a²b
=2×2×(-1)²+2×(-1)+1/2×2²×(-1)
=4-2-2
=0