(a) Let A e Max (R) be defined by a=i+j and Be M4x3(R) be defined by bij = 12-j. Compute the product ABAB. (b). Let A e M(R) defined by aj ij and p(x):= 2+2r-r+2 e R[r] a real polynomial. Compute p(A): A+2A-A+212. (c) If Ce M.(R) such that C+ I, is the zero matrix, prove that C is invertible.