## Linear Algebra and Its Applications (5th Edition)

$$x_1 \begin{bmatrix} 4 \\ 1 \\ 8 \end{bmatrix} + x_2 \begin{bmatrix} 1 \\ -7 \\ 6 \end{bmatrix} + x_3 \begin{bmatrix} 3 \\ -2 \\ -5 \end{bmatrix} = \begin{bmatrix} 9 \\ 2 \\ 15 \end{bmatrix}$$
The vector on the right hand side holds the constants from the right hand sides of each of the equations. The vectors multiplied by $x_1$, $x_2$ and $x_3$ hold the coefficients of each variable in the three equations.