6. [2 points for correct; 0 for incorrect answer or no answer Suppose n x n matrices A, B are both invertible, and a is a n x 1 vector. Answer "True" or "False" for the following: A. Ax = 0 might have a non trivial solution. B. (A+ B)2 = A2 + 2AB + B2 must be true C. B" AB must be invertible D. There always exists a matrix C so that ABC = I E. Suppose (A - B) is also invertible. Then I - A-B must be invertible