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## Homework Statement

Harris stands at point A and wants to take a picture of bird located at point B. Because there is wall, he has to direct his camera to mirror located 3.7 m to the north from his position. What is the focal length of his camera so that he can take a clear picture of the bird?

## Homework Equations

1/f = 1/do + 1/di

f = focal length

do = distance of object

di = distance of image

## The Attempt at a Solution

Harris will see the object as if it appears behind the mirror, let say at position B' (reflection of point B to the mirror), with distance 2.1 m. I try to find object distance (AB') by using Pythagorean theorem (triangle ABB'):

(4.3)

^{2}+ (3.7 + 2.1)

^{2}= (BB')

^{2}

Is it true the object distance is BB'? If yes, then how to find the distance of image (di)? We have to know di first if we want to calculate f.

Thanks