Answer
$[3\ \ 0\ -6\ -2]$
Work Step by Step
If $A$ is an $m\times\boxed{n }$ matrix and $B$ is an $\boxed{n }\times k$ matrix,
then the product $AB$ is the $m\times k$ matrix whose $ij-$th entry is the product
$(AB)_{ij}=[a_{i1}\ a_{i2}\ a_{i3}\ \ldots\ a_{in}]\left[\begin{array}{l}
b_{1j}\\
b_{2j}\\
b_{3j}\\
\vdots\\
b_{nj}
\end{array}\right]$
$=a_{i1}b_{1j}+a_{i2}b_{2j}+a_{i3}b_{3j}+\cdots+a_{in}b_{nj}$.
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Here,
A is a 1$\times$2 matrix, B is a 2$\times$4 matrix
AB is defined, and is a 1$\times$4 matrix.
$(AB)_{11}=-1(-3)+1(0)=3$
$(AB)_{12}=-1(1)+1(1)=0$
$(AB)_{13}=-1(4)+1(-2)=-6$
$(AB)_{14}=-1(3)+1(1)=-2$
$AB=[3\ 0\ -6\ -2]$
