Concave lens equation: why does n₂ cancel in the derivation?

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Daniiel
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Hey
this is a pretty straight forward equation derivation, but when i do it and compare it to the solutions, mine is different to theirs.
The equation is
[PLAIN]http://img213.imageshack.us/img213/9790/ddaaad.jpg where n1=1
for a concave lens (fish in a fish bowl) so r is negative

solving for i

they get, r/(n2+1)

and i get n2r/(n2+1)

there answer seems right for the question, but I am just not sure how they canceled the n2
 
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Post the actual problem in the book.
 
[PLAIN]http://img228.imageshack.us/img228/593/dsdsdsaas.jpg

p = r/2 n2 = water
 
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The fish is inside the bowl. So the formula becomes

n1/p + n2/i = (n1 - n2)/r

Here n1 = 1.33 and n2 = 1.

Now simplify and find i.
 
oh right
thanks a lot