Question 636091
The matrix 


<img src="http://latex.codecogs.com/gif.latex?\left[ \begin{array}{cccc|c} 9 & 1 & 0 & 8& 6\\ -1 & 5 & 1 & 0 & -12 \\ 7 & 0 & 0 & 3 & -9 \\ 0 & 4 & 0 & -4 & 8 \\ \end{array}\right]" title="\left[ \begin{array}{cccc|c} 9 & 1 & 0 & 8& 6\\ -1 & 5 & 1 & 0 & -12 \\ 7 & 0 & 0 & 3 & -9 \\ 0 & 4 & 0 & -4 & 8 \\ \end{array}\right]" />


turns into the system of equations


<img src="http://latex.codecogs.com/gif.latex?\begin{array}{rl} 9x+y+8w &= 6\\ -x+5y+z &= -12 \\ 7x+3w &= -9 \\ 4y-4w &= 8 \end{array}" title="\begin{array}{rl} 9x+y+8w &= 6\\ -x+5y+z &= -12 \\ 7x+3w &= -9 \\ 4y-4w &= 8 \end{array}" />


Note: there are 4 columns before the augmented part (or column), so I had to use 4 variables instead of 3. Maybe there's a typo somewhere in the problem?