1. The problem statement, all variables and given/known data A. If the equation Ax=0 has only the trivial solution, then A is row equivalent to the nxn identity matrix. B. If the columns of A span R^n, the columns are linearly independent. C. If A is an nxn matrix, then the equation Ax=b has at least one solution for each b in R^n. D. If the equation Ax=0 has a nontrivial solution, then A has fewer than n pivot positions. E. If A^T is not invertible, then A isn't invertible? 2. Relevant equations 3. The attempt at a solution A. True B. False D. True I think. As for the rest of them I would like to discuss them with you.