1. The problem statement, all variables and given/known data Let Amn be a matrix representation of some operator A in the basis |φn> and let Unj be a unitary operator that changes the basis |φn> to a new basis |ψj>. I am asked to write down the matrix representation of A in the new basis. 2. Relevant equations 3. The attempt at a solution Should I try to evaluate <m|UnjA|n>? Is that how this should be approached? I know that Unj|φn>=|ψj>.