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    The definition I got is that B is called dense in A if \forall x \in A, \forall \epsilon >0, we have B_{\epsilon}(x) \cap B \neq \emptyset

    Not sure where to begin as the Cauchy part throws me off any ideas that I get.
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    I think a good place to start is to show (or explain why) for any point x and integer q >0 we can find p s.t. |x-p/q| < 1/q.
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    As above: just going to mention that to show DFranklin's result you'll want to use the archimidean property.
 
 
 
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