(A,I)=
(5 2 0 0 1 0 0 0
2 1 0 0 0 1 0 0
0 0 8 3 0 0 1 0
0 0 5 2 0 0 0 1)
(1 0 0 0 1 -2 0 0
2 1 0 0 0 1 0 0
0 0 -2 -1 0 0 1 -2
0 0 5 2 0 0 0 1)
(1 0 0 0 1 -2 0 0
0 1 0 0 -2 5 0 0
0 0 -4 -2 0 0 2 -4
0 0 5 2 0 0 0 1)
(1 0 0 0 1 -2 0 0
0 1 0 0 -2 5 0 0
0 0 1 0 0 0 2 -3
0 0 0 2 0 0 -10 16)
1 0 0 0 1 -2 0 0
0 1 0 0 -2 5 0 0
0 0 1 0 0 0 2 -3
0 0 0 1 0 0 -5 8)
A-1=
(1 -2 0 0
-2 5 0 0
0 0 2 -3
0 0 -5 8)