r3-2r1,r1-2r2,r4-r2
0 1 -1
1 1 2
0 1 -3
0 2 -1
r3-r1,r4-2r1
0 1 -1
1 1 2
0 0 -2
0 0 1
r3+2r4
0 1 -1
1 1 2
0 0 0
0 0 1
交换行
1 1 2
0 1 -1
0 0 1
0 0 0
秩 = 3