An optical fiber consists of a cylindrical core with refractive index \(n_1\) surrounded by a cladding with refractive index \(n_2\), where \(n_1 > n_2\). The fiber is surrounded by a medium with refractive index \(n_0\), where \(n_0 < n_1\). The front entrance face of the core is flat and perpendicular to the central axis of the fiber. Light strikes the entrance face at an angle of incidence \(\theta_0\) relative to the normal of the entrance face, refracts into the core, and then strikes the core-cladding boundary. Which of the following expressions represents the maximum angle of incidence \(\theta_{\text{max}}\) at the entrance face such that the ray undergoes total internal reflection at the core-cladding boundary?