Question

The minor of the element 3 in the determinant $\left|\begin{array}{ccc}1& 2& 3\\ 4& 5& 6\\ 7& 8& 9\end{array}\right|$ is ___

Answer 1

We know that minor is the determinant of the square matrix formed by deleting the row and column corresponding to the element from the original matrix.

So by following the mentioned rule to calculate the minors, the minor for the element 3 i.e. third element of first row shall be calculated by deleting the first row and third column and then taking the determinant of the remaining matrix.

So minor for 3 will be $\left|\begin{array}{cc}4& 5\\ 7& 8\end{array}\right|$ = 8 $\times$ 4 -7 $\times$5 = 32-35 = -3 which is the correct answer.