5. (5 points) For each of the following, answer either true (with a reason) or false (with a counterexample). (a) If Q is an orthogonal matrix, then Q'1 is orthogonal. (b) If Q is an orthogonal matrix, then QT is orthogonal. (c) If Q1 and Q2 are orthogonal matrices, then C2ng is orthogonal. ) (d If Q is a matrix with orthonormal columns (need not be square), then ||az|| = ||a3|| for every :13