Question

if | A| = -7 find x where A ( 3 X 2 1)

Answer 1

$$A=\begin{pmatrix} 3 & x \\ 2 & 1 \end{pmatrix}$$

$$|A|=\begin{vmatrix} 3 & x \\ 2 & 1 \end{vmatrix}=3(1)-2x=3-2x=-7$$

$$2x=10$$

$$x=5$$