Solve the following system of equations by matrix method: `x+y+z=3,\ \ 2x-y+z=-1,\ \ 2x+y-3z=-9`

Explanation

To solve the system of equations using the matrix method, we will follow these steps:

### Given Equations:
1. \( x + y + z = 3 \) (Equation 1)
2. \( 2x - y + z = -1 \) (Equation 2)
3. \( 2x + y - 3z = -9 \) (Equation 3)

### Step 1: Write the system in matrix form \( AX = B \)
...