UPSC NDA I 2023 General Ability Solved Paper

Shown in the figure are two plane mirrors XY and YZ(XY‌⟂‌YZ) joined at their edge. Also shown is a light ray falling on one of the mirrors and reflected back parallel to its original path as a result of this arrangement. The two mirrors are now rotated by an angle θ to their new position X′‌YZ‌Z′, as shown. As a result the new reflected ray is at an angle α from the original reflected ray. Then :