Let \(A = \begin{bmatrix} \cos^2 x & \sin^2 x \\\ \sin^2 x & \cos^2 x \end{bmatrix}\) and \(B = \begin{bmatrix} \sin^2 x & \cos^2 x \\\ \cos^2 x & \sin^2 x \end{bmatrix}\). Then the determinant of the matrix A + B is