已知|a-2|+（b+1）^2=0,
所以 a-2=0 a=2
b+1=0 b=-1
代数式3a^2b+ab^2-3a^2b+5ab+ab^2-4ab+1/2a^2b是
=ab+2ab^2+1/2a^2b
=-2+4-2
=0