A plane mirror is placed 22.5cm in front of a concave mirror of focal length 10cm as shown in the figure. Find the distance of the object (in cm) from the concave mirror where it can be placed so that the first image in both the mirrors coincide.

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TestHub · Accepted Answer

For coincidence, trace the plane-mirror image and the concave-mirror image using the mirror formula.

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

Using mirror separation 22.5 cm and f = 10 cm gives object distance 15 cm from the concave mirror.

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