Answer
$\left[\begin{array}{rrr}
-4 & -7 & -1\\
9 & 17 & 0
\end{array}\right]$
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
$(AB)_{ij}=[a_{i1}\ a_{i2}\ a_{i3}\ \ldots\ a_{in}]\left[\begin{array}{l}
b_{1j}\\
b_{2j}\\
b_{3j}\\
\vdots\\
b_{nj}
\end{array}\right]$
$=a_{i1}b_{1j}+a_{i2}b_{2j}+a_{i3}b_{3j}+\cdots+a_{in}b_{nj}$.
-------
Here,
A is a $2\times 3$ matrix, B is a $3\times 3$ matrix
AB is defined, and is a $2\times 3$ matrix.
$(AB)_{11}=1(0)+0(1)-1(4)=-4$
$(AB)_{12}=1(1)+0(0)-1(8)=-7$
$(AB)_{13}=1(-1)+0(1)-1(0)=-1$
$(AB)_{21}=1(0)+1(1)+2(4)=9$
$(AB)_{22}=1(1)+1(0)+2(8)=17$
$(AB)_{23}=1(-1)+1(1)+2(0)=0$
$AB=\left[\begin{array}{lll}
-4 & -7 & -1\\
9 & 17 & 0
\end{array}\right]$
