2-r1,r4+5r1
1 3 -1 2
0 -8 4 -6
0 2 1 -1
0 16 -2 7
r2+4r3,r4-8r3
1 3 -1 2
0 0 8 -10
0 2 1 -1
0 0 -10 15
r4+(10/8)r2
1 3 -1 2
0 0 8 -10
0 2 1 -1
0 0 0 5/2
= -2*8*(5/2)
= -40.
2-r1,r4+5r1
1 3 -1 2
0 -8 4 -6
0 2 1 -1
0 16 -2 7
r2+4r3,r4-8r3
1 3 -1 2
0 0 8 -10
0 2 1 -1
0 0 -10 15
r4+(10/8)r2
1 3 -1 2
0 0 8 -10
0 2 1 -1
0 0 0 5/2
= -2*8*(5/2)
= -40.