②a★b= 1/2a+ 1/2b (that is, half a plus half b).

③(-2)★(-4)=0.5×(-2)+0.5×(-4)=-3

④ Yes, because the coefficients before A and B are the same.

You've written the form in a mess. I have studied your form for a long time. In fact, the topic is not difficult. I hope I can catch up with you! By the way, 1234 in the first line (column) stands for A or B, so the blank in the first line need not be filled, it is just a title!