Practicing Success
If $a_{ij}$ represents the elements of $i^{th}$ row and $j^{th}$ column and $A_{ij}$ is the corresponding cofactor, then for the matrix $A=\begin{bmatrix} 1 & -1 & 0\\2 & 0 & 1\\3 & 4 & 2\end{bmatrix}$ the value of $a_{11}A_{21}+a_{12}A_{22}+a_{12}A_{22}+a_{13}A_{23}$ is : |
-3 -5 3 5 |
-5 |
The correct answer is Option (2) → -5 $A=\begin{bmatrix} 1 & -1 & 0\\2 & 0 & 1\\3 & 4 & 2\end{bmatrix}$ $C_{11}=-4,C_{12}=-1,C_{13}=8$ $C_{21}=2,C_{22}=2,C_{23}=-7$ $C_{31}=-1,C_{32}=-1,C_{33}=2$ so $Adj\,A=\begin{bmatrix}-4&-1&8\\2&2&-7\\-1&-1&2\end{bmatrix}^T=\begin{bmatrix}-4&2&-1\\-1&2&-1\\8&-7&2\end{bmatrix}$ $a_{11}A_{21}+a_{12}A_{22}+a_{12}A_{22}+a_{13}A_{23}=1×(-1)+-1×2+-1×2+0×-1$ $=-1-2-2=-5$ |