Explanation:
There are some conventions while solving the problems based on mirrors. All parameters are taken like x-y coordinate system.
All the measurements are done from the optical centre of the mirror.
[tex]d_i[/tex] is the image distance
[tex]d_o[/tex] is the object distance
[tex]-d_i[/tex] is the image distance which is formed behind the mirror.
[tex]-d_o[/tex] is the object distance when an object is placed behind the mirror.
So, [tex]-d_i[/tex] shows the image that is located behind the mirror. Hence, this is the required solution.
