A is an n×n matrix. 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. A matrix A is not invertible if and only if 0 is an eigenvalue of A. C. To find the eigenvalues of A, reduce A to echelon form. D. A number c is an eigenvalue of A if and only if the equation (A−c)x=0 has a nontrivial solution x. E. If Ax=x for some vector x, then is an eigenvalue of A.