\begin{definition}[Definition:Apotome of Medial/First Apotome]
Let $a, b \in \set {x \in \R_{>0} : x^2 \in \Q}$ be two rationally expressible numbers such that $a > b$ be in the forms:
:$a = k^{1/4} \rho$
:$b = k^{3/4} \rho$
where:
:$\rho$ is a rational number
:$k$ is a rational number whose square root is irrational.
Then $a - b$ is a '''first apotome of a medial'''.
{{:Euclid:Proposition/X/74}}
\end{definition}