For $\Delta = \begin{vmatrix}x & 1 & 2 \\ 3 & 0 & 1 \\ 2 & 4 & x\end{vmatrix}$, what is the cofactor of the element in row 1, column 2?

Explanation

1. 01

   Delete row 1 and column 2: $M_{12} = \begin{vmatrix} 3 & 1 \\ 2 & x \end{vmatrix} = 3x - 2$.

2. 02

   $A_{12} = (-1)^{1 + 2}(3x - 2) = 2 - 3x$.