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Q.
An object is placed symmetrically between two plane mirrors, inclined at an angle of $72^{\circ}$, then the total number of images observed is
Ray Optics and Optical Instruments
Solution:
For number of images formed from plane mirror
$m=\frac{360}{\theta}=\frac{360}{72}=5$
If it was at any other point the number of images $(n)=m$ but this is not so.
Since it is placed symmetrically :
$n=m-1$
or $n=5-1$
or $n=4$ images