Chapter 3 Linear Systems and Matrices - 3.8 Use Inverse Matrices to Solve Linear Systems - Guided Practice for Example 1 - Page 210: 2

$A^{-1}=\begin{bmatrix} \frac{2}{3} &\frac{-5}{12}\\ \frac{1}{3} & \frac{-1}{12} \end{bmatrix}$

$A^{-1}=\frac{1}{-8+20}\begin{bmatrix} 8 & -5\\ 4 & -1 \end{bmatrix}=\frac{1}{12}\begin{bmatrix} 8 & -5\\ 4 & -1 \end{bmatrix}=\begin{bmatrix} \frac{2}{3} &\frac{-5}{12}\\ \frac{1}{3} & \frac{-1}{12} \end{bmatrix}$