17 If A is n*n matrix with real entries,then (a) A has n eigenvalues exactly. 想请问这选项该不该选 18 If A can be QR factorized,then (a) A has linearly independent eigenvectors. (b) The columns of Q are orthonormal basis for ColA. (c)(Q^T)*Q=I. (d)A=QR and (Q^T)*Q=I => (Q^T)*A = (Q^T)*Q*R => (Q^T)*A = R =>Q*(Q^T)*A = QR = A =>Q(Q^T) = I. (e)R is an upper triangular invertible matrix with positive entries on its upper triangel. 想请教这题的答案