Question

$A=\left\{\begin{array}{cc}8& 9\\ 10& 11\end{array}\right\}$, then cofactor of $a_{12}$ is:

• A. 11
• B. 10
• C. -11
• D. -10

Answer 1

The correct option is D -10

By property of cofactor (2),
$A=\left[\begin{array}{cc}8& 9\\ 10& 11\end{array}\right]$
minor of $a_{12}=M_{12}=10$
So, cofactor of $a_{12}=M_{12}(-1{)}^{1+2}=-M_{12}=-10$