Two plane mirror are placed back to back. They are then opened out slowly to form a wedge, their reflecting surfaces lying on the outside. A beam of parallel light becomes incident on the edge of the wedge. The two beams reflected from its face are found to make an angle of $120°$ with each other. Determine the angle between the mirrors.

Two mirrors, one concave and the other convex, and placed coaxially with their reflecting surfaces facing each other. Their radii of curvature are equal, say $R$, and the distance between them is $2R$. A point object is placed on the axis in such a way that it coincides with its image formed by two reflections, the first reflection being by the convex mirror. Determine the position of the object. Where will be the image formed if the first reflection takes place at the concave mirror ?