Answer
$\begin{bmatrix} 13\\25\end{bmatrix}$
Work Step by Step
Since, the dimensions of matrix $A$ is $2 \times 2$ and that of matrix $B$ is $2 \times 1$. Therefore, the number of columns of matrix-$A$ will be same as the number of rows of the matrix-$B$. when we take their product $AB$.
$AB=\begin{bmatrix} 1 &2\\3&4\end{bmatrix} \begin{bmatrix} -1 \\7\end{bmatrix} \\=\begin{bmatrix} 1(-1)+(2)(7)\\(3)(-1)+(4)(7) \end{bmatrix}\\=\begin{bmatrix} 13\\25\end{bmatrix}$
Thus, the product of $AB=\begin{bmatrix} 13\\25\end{bmatrix}$
