Existence of Canonical Form of Rational Number

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Let $r \in \Q$.


$\exists p \in \Z, q \in \Z_{>0}: r = \dfrac p q, p \perp q$

That is, every rational number can be expressed in its canonical form.


We have that the set of rational numbers is the field of quotients of the set of integers.

From Divided by Positive Element of Field of Quotients:

$\exists s \in \Z, t \in \Z_{>0}: r = \dfrac s t$

Now if $s \perp t$, our task is complete.

Otherwise, let:

$\gcd \set {s, t} = d$

where $\gcd \set {s, t}$ denotes the greatest common divisor of $s$ and $t$.

Let $s = p d, t = q d$.

We have that $t, d \in \Z_{>0}$

Therefore $q \in \Z_{>0}$ also.

From Integers Divided by GCD are Coprime:

$p \perp q$


\(\ds \frac s t\) \(=\) \(\ds \frac {p d} {q d}\)
\(\ds \) \(=\) \(\ds \frac p q \frac d d\)
\(\ds \) \(=\) \(\ds \frac p q 1\)
\(\ds \) \(=\) \(\ds \frac p q\)


$r = \dfrac p q$

where $p \perp q$ and $q \in \Z_{>0}$.


Also see