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how to show this is a dense set?

I want to show that

Given any irrational number $\alpha\in \mathbb{R}$, the set $\displaystyle S=\{ m+n\alpha : m,n\in Z \}$ is dense in $\mathbb{R}$.

Thanks in advance!

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marked as duplicate by Chris Eagle, Davide Giraudo, David Mitra, Rudy the Reindeer, Ilya Jul 31 '12 at 16:15

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1 Answer 1

Kronecker's Theorem gives us that the set $\{ma\}_{m \in \mathbb{Z}}$ is dense in $(0,1)$ for irrational $a$, and hence, that the set $\{n+ma\}_{m,n \in \mathbb{Z}}$ is dense in $\mathbb{R}$.

If you want to prove Kronecker's Theorem, you may use Weyl's Criterion, which proves more strongly, that the said sequence is equidistributed too!

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Please write the statement of Kronecker's theorem! –  Kns Jul 31 '12 at 16:12
    
I've edited to give the link of Kronecker's Theorem. Hope this helps. –  Rijul Saini Jul 31 '12 at 16:15
    
With $a=\pi$, I don't find a single integer $m$ so that $0<ma<1$. That's quite the opposite of "dense in $(0,1)$". –  celtschk Jul 31 '12 at 16:15
1  
@celtschk The notation $\{ma\}$ is the decimal part of $ma$. –  David Mitra Jul 31 '12 at 16:17
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OK, maybe when using $\{\}$ in any other way than to denote sets, it would be a good idea to explicitly say that :-) Especially since your second use obviously is using it just to denote a set (the set of fractional parts of $n+ma$ definitely is not dense in $\mathbb{R}$). –  celtschk Jul 31 '12 at 16:24

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