$A$ ray of light is incident on the first face of an equilateral glass prism at an angle of incidence '$i$'. The emergent ray just grazes along the adjacent face. The refractive index of the prism is $\sqrt{2}$. The value of the angle of incidence at the first face is $(\sin 45^{\circ} = 1/\sqrt{2}, \sin 90^{\circ} = 1)$.

• A
  $\sin^{-1}(\sqrt{2} \sin 15^{\circ})$
• B
  $\sin^{-1}(\frac{\sin 30^{\circ}}{\sqrt{2}})$
• C
  $\cos^{-1}(\sqrt{2} \sin 20^{\circ})$
• D
  $\tan^{-1} \sqrt{2 \sin 15^{\circ}}$