Question 683916
x-4y+4z=-9
2x-9y+8z=1
6y-9z=-1 



1x-4y+4z=-9
2x-9y+8z=1
0x+6y-9z=-1 



1x+(-4)y+4z=-9
2x+(-9)y+8z=1
0x+6y+(-9)z=-1 



<img src="http://latex.codecogs.com/gif.latex?\large \left[ \begin{array}{c c c | c} 1 & -4 & 4 & -9\\ 2 & -9 & 8 & 1\\ 0 & 6 & -9 & -1 \end{array}\right ]" title="\large \left[ \begin{array}{c c c | c} 1 & -4 & 4 & -9\\ 2 & -9 & 8 & 1\\ 0 & 6 & -9 & -1 \end{array}\right ]" />


Feel free to ask me any questions you have. Thanks.