向量组的线性相关性问题

(a1,a2,a3,a4)=
2 -1 1 -1
1 1 1 -2
4 -6 -2 2
3 6 7 -9
r1-2r2,r3-4r2,r4-3r2
0 -3 -1 3
1 1 1 -2
0 -10 -6 10
0 3 4 -3
r3-3r1,r4+r3
0 -3 -1 3
1 1 1 -2
0 -1 -3 1
0 0 3 0
-->
0 -3 0 3
1 1 0 -2
0 -1 0 1
0 0 1 0
-->
0 0 0 0
1 1 0 -2
0 -1 0 1
0 0 1 0
a1,a2,a3 线性无关
a1,a2,a3,a4 线性相关