MCQ
For which of the following element in the determinant $\triangle=\begin{bmatrix}5&-5&8\\6&2&-1\\5&-6&8\end{bmatrix},$ the minor and the cofactor both are zero.
  • A
    $-5$
  • $2$
  • C
    $-6$
  • D
    $8$

Answer

Correct option: B.
$2$
Consider the element $2$ in the determinant $\triangle=\begin{bmatrix}5&-5&8\\6&2&-1\\5&-6&8\end{bmatrix}$
The minor of the element $2$ is given by
$\therefore\text{M}_{22}=\begin{bmatrix}5&8\\5&8\end{bmatrix}=40-40=0$
$\Rightarrow\text{A}^{22}=(-1)^2+2 (0)=0.$

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