应该是(a-2)^2+(b+1)^2=0,a=2,b=-1,
3a^2b+ab^2-3a^2b+5ab+ab^2-4ab+2/1 ab^2=5/2a^2b+ab=5-2=3题上没说a=多少b=多少由(a-2)^2+(b+1)^2=0,推出a=2,b=-1