A light ray moving through air strikes an air-glass boundary. The angles between the incident ray, the refracted ray and the boundary are shown. Which equation is used to determine the refractive index $n$ of the glass?
- A$n = \dfrac{\sin 40^\circ}{\sin 26^\circ}$
- B$n = \dfrac{\sin 40^\circ}{\sin 64^\circ}$
- C$n = \dfrac{\sin 50^\circ}{\sin 26^\circ}$
- D$n = \dfrac{\sin 50^\circ}{\sin 64^\circ}$