... either a = 0 and b = 0 or b = 0 and a = 0. In the first case 0 = ad + bc = bc and therefore, c = 0; in the second case ad = 0 and, therefore, d = 0. In either case we get a noninvertiblematrix ... unitary and, therefore, the absolute value of its eigen-values is equal to 1.22.1. The eigenvalues of an orthogonal matrix belong to the unit circle centeredat the origin and the eigenvalues ... believe that they will beof interest to many readers.I assume that the reader is acquainted with main notions of linear algebra:linear space, basis, linear map, the determinant of a matrix. Apart...