c1c3 (-1)*
1 -5 2 2
-1 7 -3 4
2 -9 5 7
1 -6 4 2
r2+r1, r3-2r1,r4-r1
1 -5 2 2
0 2 -1 6
0 1 1 3
0 -1 2 0
r2-2r3,r4+r3
1 -5 2 2
0 0 -3 0
0 1 1 3
0 0 3 3
r4+r2, r2r3 *(-1) 与之前的-1抵消
1 -5 2 2
0 1 1 3
0 0 -3 0
0 0 0 3
行列式 = -9
c1c3 (-1)*
1 -5 2 2
-1 7 -3 4
2 -9 5 7
1 -6 4 2
r2+r1, r3-2r1,r4-r1
1 -5 2 2
0 2 -1 6
0 1 1 3
0 -1 2 0
r2-2r3,r4+r3
1 -5 2 2
0 0 -3 0
0 1 1 3
0 0 3 3
r4+r2, r2r3 *(-1) 与之前的-1抵消
1 -5 2 2
0 1 1 3
0 0 -3 0
0 0 0 3
行列式 = -9