Check the true statements below: A. Finding an eigenvector of A might be difficult, but checking whether a given vector is in fact an eigenvector is easy. B. To find the eigenvalues of A, reduce A to echelon form. C. A number c is an eigenvalue of A if and only if the equation (A D. A matrix A is not invertible if and only if 0 is an eigenvalue of A. E. If Ax = 1x for some vector x, then 1 is an eigenvalue of A. cI)x = 0 has a nontrivial solution x.