Hi, I'm looking for a proof of the following theorem: If A is a hermitian matrix with eigenvalues a_1, a_2...a_n, then the secular equation holds: (A - a_1)(A - a_2)...(A - a_n) = 0. The proof escapes me right now but I think it has to do with diagonalizing the hermitian matrix. I'm just struggling to put together the details. Assume non-degeneracy. Thanks.