1. The problem statement, all variables and given/known data Consider an n x m matrix A with n >= m. If all columns of A are orthonormal, then A'A = I. What can you say about AA'? Where A'A = transpose(A)*A and AA' = A*transpose(A) 2. Relevant equations 3. The attempt at a solution For the case that n = m: A is square. Since the columns of A are normalized, and the set of vectors contained in A is orthogonal, we can call A orthogonal. So, A'A = I and AA' = I For the case that n > m: I'm lost here... any hints? What should I be looking up in the books to understand this?