First Apotome/Example
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Example of First Apotome
Let $a, b \in \set {x \in \R_{>0} : x^2 \in \Q}$ be two rationally expressible numbers such that $a - b$ is an apotome.
By definition, $a - b$ is a first apotome if and only if:
- $(1): \quad a \in \Q$
- $(2): \quad \dfrac {\sqrt {a^2 - b^2}} a \in \Q$
where $\Q$ denotes the set of rational numbers.
Let $a = 9$ and $b = \sqrt {17}$.
Then:
\(\ds \frac {\sqrt {a^2 - b^2} } a\) | \(=\) | \(\ds \frac {\sqrt {81 - 17} } 9\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \frac {\sqrt {64} } 9\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \frac 8 9\) | \(\ds \in \Q\) |
Therefore $9 - \sqrt {17}$ is a first apotome.