SOLUTION: The lens equation for a camera is 1/f= 1/di+1/d0, where f is the focal length of the lens, di is the distance between the lens and the film, and d0 is the distance between the lens

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Question 276564: The lens equation for a camera is 1/f= 1/di+1/d0, where f is the focal length of the lens, di is the distance between the lens and the film, and d0 is the distance between the lens and the object. For a certain camera, an object that is 18 cm from the lens is in focus when the lens is 9 cm from the film. What is the focal length of the lens?
this is what i worked it out too-> 1/f= 4/9

Answer by jsmallt9(3758)   (Show Source): You can put this solution on YOUR website!

You are given that the distance from the lens to the object, , is 18 and the the distance from the lens to the film, , is 9. Substituting these into the equation we get:

There are several ways to solve for f:
I am going to use the last method. The LCD of all three fractions is 18f. So multiply both sides by 18f:

On the right side we need to use the Distributive Property to multiply:

In each term the denominator cancels:

leaving:

Simplify the right side:

Dividing both sides by 3 we get:

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