Answer
474
Work Step by Step
We are given:
$A=\begin{bmatrix}
1 & 2 & -1\\
2& 1 & 4
\end{bmatrix}$
$B=\begin{bmatrix}
2 & 1\\
5& -2\\
4 & 7
\end{bmatrix}$
then $AB=\begin{bmatrix}
8 & -10\\
25& 28
\end{bmatrix}$
Hence here:
$\det(AB)=8.28-25.(-10)=474$
