Question

If $A=\begin{bmatrix}1&1&0\\\ 2&1&5\\\ 1&2&1\end{bmatrix}$, then $a_{11}A_{21} +a_{12}A_{22}+a_{13}A_{23}$ is equal to

• A. $1$
• B. $0$
• C. $-1$
• D. $2$

Answer 1

Answer: (B)

$0$

Answer 2

Given, $A=\begin{bmatrix}1&1&0\\\ 2&1&5\\\ 1&2&1\end{bmatrix}$
We know that, the sum of the product of element other than the corresponding cofactor
is zero
$\therefore a_{11}A_{21}+a_{12}A_{22}+a_{13}A_{23}=0$