Question:
If $A=\left[\begin{array}{lll}5 & 3 & 8 \\ 2 & 0 & 1 \\ 1 & 2 & 3\end{array}\right]$. Write the cofactor of the element $a_{32}$.
Solution:
Minor of $a_{32}=M_{32}=\left|\begin{array}{ll}5 & 8 \\ 2 & 1\end{array}\right|=5-16=-11$
Cofactor of $a_{32}=A_{32}=(-1)^{3+2} M_{32}=11$
Hence, the cofactor of the element $a_{32}$ is 11 .