1. The problem statement, all variables and given/known data Let the commutator [A,B] = cI, I the identity matrix and c some arbitrary constant. Show [A,Bn] = cnBn-1 2. Relevant equations [A,B] = AB - BA 3. The attempt at a solution So I have started off like this: [A,Bn] = ABn - BnA = cI I'm not sure where to go from here.