21. Which of the following statements are NOT correct? (A) Let A be a real n x n matrix. If A2 is invertible, then and A3 are invertible. (B) If A and B are invertible, then so is A+B, and . (C) Let A be a real m x n matrix and B a real n x m matrix. Then trace(AB) = trace(BA). (D) Let A be a real m x matrix and B a real n x m matrix. Then det(AB) = det(BA). (E) Let A and B be real n x n matrices. Then AB = BA.