A plane mirror and a concave mirror are arranged as shown in figure and $O$ is a point object. Find the position of image formed by two reflections w.r.t A, first one taking place at concave mirror.

 

For concave mirror,

$$\begin{gathered} \frac{1}{v}+\frac{1}{u}=\frac{1}{f} \\ or \frac{1}{v}-\frac{1}{110}=-\frac{1}{100} \\ or v=-1100 cm. \end{gathered}$$

Thus first image $I_1$ is formed at $100 cm$ behind the plane mirror. This acts as virtual object for the plane mirror. If plane mirror would had been in vertical position as shown in figure(a), the image of $I_1$ had been formed at $I_2$, $100 cm$in front of plane mirror. But since the plane mirror has been rotated $45°$ in clockwise direction. Hence, all the reflected rays will rotate $90°$ in same sense i.e clockwise and image will be formed $100 cm$ vertically below A.