# Is (-4,1), (1,8), (-4,-2) a function?

No, the first elements of the pairs are not distinct, yielding two different values for $f \left(- 4\right)$.
$\left(x , y\right)$ with $x$ mapping into $y$ with the set
$\textcolor{w h i t e}{\text{XXXX}}$$\left\{\begin{matrix}- 4 & 1 \\ 1 & 8 \\ - 4 & 2\end{matrix}\right\}$
since $x = - 4$ maps into more than one value
(it maps into both $1$ and $2$).