1 3 1 4
3 1 4 4
0 0 2 1
1 1 1 4
r2-3*r1:
1 3 1 4
0 -8 1 -8
0 0 2 1
1 1 1 4
r4-r1:
1 3 1 4
0 -8 1 -8
0 0 2 1
0 -2 0 0
r4-(1/4)r2:
1 3 1 4
0 -8 1 -8
0 0 2 1
0 0 -1/4 2
r4+(1/8)r3:
1 3 1 4
0 -8 1 -8
0 0 2 1
0 0 0 17/8
=1*(-8)*2*(17/8)
=-34