## Question

Two objects *A* and *B* when placed in turn in front of a concave mirror of focal length 7.5 cm, give images of equal size. If *A* is three times the size of*B* and is placed 30 cm from the mirror, what is the distance of *B* from the mirror?

### Solution

15 cm

It is given that *f* = –7.5 cm and *u _{A}* = –30 cm. Thus

Which gives

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