Two plane mirrors `M1` and `M2`, placed at right angles, form two sides of a container. Mirror `M1` is inclined at an angle `theta_(0)` to the horizontal. A light ray AB is incident normally on`M1`. Now the container is filled with a liquid of refractive index `mu` so that the ray is first refracted, then reflected at `M1`. The ray is next reflected at `M2` and then comes out of the liquid surface making an angle `theta` with the normal to the liquid surface. Find `theta`.