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## Homework Statement

A convex lens forms an image 8.96 mm on a screen. Keeping the screenand the object fixed, the lens is moved through a distance of 15.4 cm and a sharp image of the object is again observed on the screen. If the length of the second image is 3.54 cm, calculate the focal length of the lens.

## Homework Equations

1/f = 1/u + 1/v

M = v/u = Hi/Ho

## The Attempt at a Solution

Hi1 = 0.896, Hi2 = 3.54

u2 = u1 + 15.4, v2 = v1 - 15.4 (Could be plus or minus for both).

1/u1 = 0.896/Ho

=> v2/u2 = 3.54/Ho = (v1-15.4)/(u1+15.4)

=> 1/(u1+15.4) + 1/(v1-15.4) = 1/u1 + 1/u2

I've tried solving from there, but always end up with negatives or weird answers. The book's answer was 10.3. Any hints or help please? :P