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## Homework Statement

We have a convex lens with a focal length of 8cm, which is 12cm from the second converging lens that has a focal length of 4cm. An object is 12cm from the first lens. Where is the final image?

## Homework Equations

1/d

_{o}+ 1/d

_{i}= 1/f

## The Attempt at a Solution

So i know I have to apply the lens equation to both lens, starting with the first lens:

1/d

_{i}= 1/f - 1/d

_{o}= 1/8cm + 1/12cm = 1/24cm

d

_{i1}=+24cm

here is where I get confused. Applying the lens equation to the second lens

I did:

1/d

_{i2}= 1/f - 1/d

_{o}(do here equals d

_{i1})

1/d

_{i2}= 1/4cm - 1/12cm = 2/12cm

d

_{i2}= +6cm

d

_{i1}+ d

_{i2}= 30cm

The answer is 27cm, I've checked my math several times and still get the incorrect answer.

any help is greatly appreciated.

Thanks