>>166
1 -1 2
1 1 1
3 1 4

1 -1 2
0 -2 -1
0 4 -2

1 -1 2
0 -2 -1
0 0 -4

1 0 0
0 1 0
0 0 1

x_1 = x_2 = x_3 = 0