1-r2-r4,r4-r2
0 0 2 1
1 -3 0 -6
0 2 -3 2
0 7 -7 12
= (-1) *
0 2 1
2 -3 2
7 -7 12
c2-2c3
0 0 1
2 -7 2
7 -31 12
= - (-62 + 49)
= 13
1-r2-r4,r4-r2
0 0 2 1
1 -3 0 -6
0 2 -3 2
0 7 -7 12
= (-1) *
0 2 1
2 -3 2
7 -7 12
c2-2c3
0 0 1
2 -7 2
7 -31 12
= - (-62 + 49)
= 13