Question:
(a) If there is an n × n matrix D such that AD = I. then there is also an n x n matrix C such that CA = 1
(b) If the columns of A are linearly independent, then the columns of A span R"
(c) If the equation Ax = b has at least one solution for each b in R". then the solution is unique for each b.
(d) If AT is not invertible, then A is not invertible.
(e) If the equation Ax = 0 has a nontrivial solution. then A has fewer than n pivot positions.