(I+A,I) =
1 1 0 1 0 0
2 1 -1 0 1 0
3 4 2 0 0 1
r2-2r1,r3-3r1
1 1 0 1 0 0
0 -1 -1 -2 1 0
0 1 2 -3 0 1
r1+r2,r3+r2,r2*(-1)
1 0 -1 -1 1 0
0 1 1 2 -1 0
0 0 1 -5 1 1
r1+r3,r2-r3
1 0 0 -6 2 1
0 1 0 7 -2 -1
0 0 1 -5 1 1
(I+A)^-1 =
-6 2 1
7 -2 -1
-5 1 1