Chapter 5 - Section 5.3 - Determinant Solution of Linear Systems - 5.3 Exercises - Page 512: 8

$-68$

The determinant for a $2 \times 2$ matrix $\begin{bmatrix} a_{11} & a_{12} \\ a_{21} & a_{22} \\ \end{bmatrix}$ can be defined as: $\text{det}= \begin{vmatrix} a_{11} & a_{12} \\ a_{21} & a_{22} \\ \end{vmatrix}=a_{11}a_{22}-a_{12}a_{21}$ Therefore, $\text{det}=\begin{vmatrix} -9 & 7 \\ 2 & 6 \\ \end{vmatrix}=(-9)(6) -(7)(2) =-54-14 =-68$ Therefore, the determinant of the given matrix is $-68$.