Study guide and 13 practice problems on:

## Matrix multiplication

The matrix product of an $n \times m$ matrix with an $m \times \ell$ matrix is an $n \times \ell$ matrix.
The $(i,j)$ entry of the matrix product $\bfA \mathbf{B}$ is the dot product of the $i$th row of $\bfA$ with the $j$th column of $\mathbf{B}$.
The $(i,j)$ entry of the matrix product $AB$ is $(AB)_{ij} = \sum_k A_{ik} B_{kj}.$