Question

If $A=\left[\begin{array}{ccc}1& -2& 3\\ 4& 0& -1\\ -3& 1& 5\end{array}\right]$, then ${(adj.A)}_{23}$ is equal to

• A. $13$
• B. $-13$
• C. $5$
• D. $-5$

Answer 1

The correct option is A $13$

$A=\left[\begin{array}{ccc}1& -2& 3\\ 4& 0& -1\\ -3& 1& 5\end{array}\right]$

${(adj.A)}_{23}=C_{32}$

So cofactor of $a_{32}$

$C_{32}={(-1)}^{3+2}(-1-12)=13$
Ans: A