1. The problem statement, all variables and given/known data Consider the so-called Spin Hamiltonian H=AS2Z+B(S2X-S2Y) for a system of spin 1. Show that the Hamiltonian in the SZ basis is the 3x3 matrix: \hbar2*[(A,0,B; 0,0,0; B,0,A)]. Find the eigenvalues using degenerate pertubation theory. 2. Relevant equations Spin Pauli Matrices 3. The attempt at a solution I don't know where to start with this since the Pauli Matrices I know are 2x2 matrices. How did the Hamiltonian become a 3x3. What am I missing? Can someone get me started?