Question

A concave mirror produces 4 times magnified real image of an object, which is placed
at a distance of 20 cm in front of it.

a) How far is the image from the mirror?
b) What is the focal length of the mirror?

Answer 1

For mirror u= f(m−1)/m

In first case, u= f(−4−1)/-4

In the second case, u+3= f(−3−1)/-3

On solving, we get f=36cm