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Jun 28, 2014 at 23:50 history edited José Hdz. Stgo. CC BY-SA 3.0
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Jun 28, 2014 at 8:54 history edited José Hdz. Stgo. CC BY-SA 3.0
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Jun 28, 2014 at 8:53 comment added José Hdz. Stgo. Apply reductio ad absurdum. Suppose that the number $\alpha$ is a rational number. We may even assume that $\alpha$ has a periodic decimal representation and that its period starts right after the decimal comma. Let $s$ denote the period length of $\alpha$. It is not difficult to establish, that for every $k\in \mathbb{N}$, the sequence $\{a_{i}\}_{i \in \mathbb{N}}$ has no more that $s$ terms of $k$ digits. Hence, $\sum_{i=1}^{\infty} \frac{1}{a_{i}} \leq \sum_{i=1}^{\infty} \frac{s}{10^{i-1}}$, which contradicts the divergence of the series $\sum_{i=1}^{\infty}\frac{1}{a_{i}}$...
Jun 28, 2014 at 8:19 comment added shadow10 Hi, could you post the solution? I couldn't find it on the web. Thanks a lot.
Jun 28, 2014 at 8:18 history edited José Hdz. Stgo. CC BY-SA 3.0
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Jun 28, 2014 at 8:10 history edited José Hdz. Stgo. CC BY-SA 3.0
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Jun 28, 2014 at 8:03 history answered José Hdz. Stgo. CC BY-SA 3.0