r3-r1-r2,r2-2r1
1 0 2 -1
0 0 -1 3
0 0 -1 -3
r3-r2
1 0 2 -1
0 0 -1 3
0 0 0 -6
r3*(-1/6),r1+r3,r2-3r3
1 0 2 0
0 0 -1 0
0 0 0 1
r1+2r2,r2*(-1)
1 0 0 0
0 0 1 0
0 0 0 1