(a1,a2,a3,b) =
1 1 1 1
1 2 -1 0
2 1 4 3
2 3 0 1
r2-r1,r3-2r1,r4-2r1
1 1 1 1
0 1 -2 -1
0 -1 2 1
0 1 -2 -1
r1-r2,r3+r2,r4-r2
1 0 3 2
0 1 -2 -1
0 0 0 0
0 0 0 0
所以 x = (2,-1,0)^T + c(-3,2,1)^T
(a1,a2,a3,b) =
1 1 1 1
1 2 -1 0
2 1 4 3
2 3 0 1
r2-r1,r3-2r1,r4-2r1
1 1 1 1
0 1 -2 -1
0 -1 2 1
0 1 -2 -1
r1-r2,r3+r2,r4-r2
1 0 3 2
0 1 -2 -1
0 0 0 0
0 0 0 0
所以 x = (2,-1,0)^T + c(-3,2,1)^T