1. The problem statement, all variables and given/known data (Commutativity) Find all 2 x 2 matrices A = [ajk ] that commute with B = [bjk], where bjk = j+k 2. Relevant equations 3. The attempt at a solution ajk = 1,1 1,1 bjk = j+k, j+k j+k, j+k I am confused about what they are trying to ask me. I understand that commute means that you can reverse it and you will come out with same outcome. I.E. like 3 x 2 = 6 and 2 x 3 = 6. Can someone give me a clue of what I should try to do.