Hello, lilikoipssn!

If is the focal length of a lens

and is the distance of an object from the lens

and is the distance of the image from the lens,

then: .

(a) Solve this equation for

Muliply by

Factor: .

(b) If cm and cm, find

We have: .

(c) If cm, and is very large, for example, 1,000,000 cm

find approximately. (This explains the name focal length)

We have: .