(b) Prove that for any two distinct invertible 2 x 2 matrices, A and B, their product cannot be the zero matrix. [2 marks] (c) Below are three invertible matrices P, Q and R. 3 O 2 3 P = Q = 2 5 R = -1 i. Show that (PQR) T = RTQTPT. [2 marks] ii. What restriction should be placed on the value of a? [1 marks]