A ray of light passes from vaccum into a medium of refractive index n. If the angle of incidence is twice the angle of refraction, then the angle of incidence is
A. `cos ^(-1)((mu)/(2))`
B. `cos ^(-1) (mu)`
C. `2 cos ^(-1) ((mu)/(2))`
D. `2 sin ^(-1) ((mu)/(2))`
