(A^T,B^T)=
5 1 -5 -8 -5 -2
3 -1 2 7 19 31
1 -2 1 0 0 0
r1-5r3,r2-3r3
0 11 -10 -8 -5 -2
0 5 -1 7 19 31
1 -2 1 0 0 0
r1-2r2
0 1 -8 -22 -43 -64
0 5 -1 7 19 31
1 -2 1 0 0 0
r2-5r1,r3+2r1
0 1 -8 -22 -43 -64
0 0 39 117 234 351
1 0 -15 -44 -86 -128
r2*(1/39),r1+8r2,r3+15r2
1 0 0 1 4 7
0 1 0 2 5 8
0 0 1 3 6 9
所以 X =
1 2 3
4 5 6
7 8 9