This is an exam question I had. I think I deserve full marks, but the prof is hard to speak too because of his english and I cant seem to find a way to convince him why I deserve full marks. So I want a second opinion, before I go to the department head.
Let A and B be nxn matrices. Can we deduce from AB=B that B = 0 or A = In?
Let B = 0.
AB = B
A0 = 0
0 = 0
therefore we can deduce that AB=B when B = 0
Let A = In
AB = B
[1,0 - 0,1]B = B
B = B
thefefore we can deduce that AB=B when A = In
(that junk in the squar bracket is an identity matrix)
(for each question, I showed each matrix as a general 2x2 matrix and expanded them to help get my message across)
From what I can understand what his complain was, is that I worked the problem out backwards. If someone can clarify this for me, give me an opinion, please let me know.
I only got 3/6 for the question. However, the exam is only out of 37 so each mark is worth quite a bit.