\begin{definition}[Definition:Multiplicative Inverse/Number]
Let $\Bbb F$ be one of the standard number fields: $\Q$, $\R$, $\C$.
Let $a \in \Bbb F$ be any arbitrary number.
The '''multiplicative inverse''' of $a$ is its inverse under addition and can be denoted: $a^{-1}$, $\dfrac 1 a$, $1 / a$, and so on.
:$a \times a^{-1} = 1$
\end{definition}