4. Show that, for any matrixes A and B, if AB is defined, then BTAT is also defined, and (AB)T = B'AT. (Hint: use either brute force or analytic method to show ((AB)))} = (BTAT)ij for all i and j. 5. Assume both A and B are square matrixes and are full rank, and AB is defined. Show (AB)-1 = B-1A-7. (Hint: use the rule for matrix multiplication and the definition for matrix inverse.)