(1.1) Suppose that A, B, C, and D are matrices with the following sizes: A B (4 x 1), (4 x 5), с (3 × 3), (3 × 5) Determine whether or not the given matrix expression is defined. If it is, then provide the size of the resulting matrix. Otherwise, clearly state the reasons why. A(DB) B(CD')', where a is a real number and Xt stands for the transpose of the matrix X. Give an example of matrices, A, B, C and D such that each product D'B and CDt is not defined.