Answer
See below
Work Step by Step
We are given:
$A=\begin{bmatrix}
1 & 3 & -1 & 2\\3 &4 & 1 &2\\7 & 1 & 4 & 6\\5 & 0&1&2
\end{bmatrix}$
The minors are:
$M_{12}=\begin{vmatrix}
3 & 1 &2\\7 & 4 & 6\\5 &1&2
\end{vmatrix}=-4$
$M_{23}=\begin{vmatrix}
1 & 3 & 2\\7 & 1& 6\\5 & 0&2
\end{vmatrix}=40$
$M_{31}=\begin{vmatrix}
3 & -1 & 2\\4 & 1 &2\\ 0&1&2
\end{vmatrix}=16$
$M_{42}=\begin{vmatrix}
1 & -1 & 2\\3 & 1 &2\\7 & 4 & 6
\end{vmatrix}$
The cofactors of the matrix A are:
$C_{12}=(−1)^{1+2}.M_{12}=-(-4)=4$
$C_{21}=(−1)^{2+1}.47
$C_{23}=(−1)^{2+3}.M_{23}=-40$
$C_{31}=(−1)^{3+1}.M_{31}=16$
$C_{42}=(−1)^{4+2}.M_{42}=12$
