# Is 0/4 undefined?

$\frac{0}{4} = 0$ is defined. $\frac{4}{0}$ is not.
If $\frac{4}{0} = k$ for some $k \in \mathbb{R}$, then we would have $0 \cdot k = 4$,
but $0 \cdot$anything$= 0 \ne 4$, so there is no such $k$.