Question

lf $A=\left[\begin{array}{ccc}1& 5& -6\\ -8& 0& 4\\ 3& -7& 2\end{array}\right]$, then the cofactor of -7=......

• A. 44
• B. 43
• C. 40
• D. 39

Answer 1

The correct option is A 44

By property of cofactor of matrix,
$A=\left[\begin{array}{ccc}1& 5& -6\\ -8& 0& 4\\ 3& -7& 2\end{array}\right]$
minor of $-7=\left|\begin{array}{cc}1& -6\\ -8& 4\end{array}\right|=4-48=-44$
So, cofactor of (-7)=minor of $(-7)\times (-1{)}^{3+2}=-[minorof(-7)]$
$=-(-44)$
$=44$