The refractive index of the cylinder is -1 and is placed in the air of μ = 1
AB is incident at B to the cylinder such that θr will be negative
θ1= θi = θr
Total deviation of the outcoming ray is 4θ1.
When the angles are measured clockwise, the planes π/3 ≤ 4θ ≤ 3 π/2
If the plane is at R π/r ≤ x ≤ 3R π/8, the light emitted from the source shall not reach the plane.