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Q.
Find the minor of $6$ and cofactor of $4$ respectively in the determinant $\Delta=\left|\begin{matrix}1&2&3\\ 4&5&6\\ 7&8&9\end{matrix}\right|\cdot$
Determinants
Solution:
Minor of $6 = M_{23}=\left|\begin{matrix}1&2\\ 7&8\end{matrix}\right|=8-14=-6$
Cofactor of $4 = c_{21}=\left(-1\right)^{2+1} \left|\begin{matrix}2&3\\ 8&9\end{matrix}\right|=-\left(18-24\right)=6$