A=
2 0 0 0
0 1 0 0
0 0 1 2
0 0 3 4
=
B 0
0 C
B^-1=
1/2 0
0 1
C^-1=
-2 1
3/2 -1/2
A^-1=
B^-1 0
0 C^-1
=
1/2 0 0 0
0 1 0 0
0 0 -2 1
0 0 3/2 -1/2
A=
2 0 0 0
0 1 0 0
0 0 1 2
0 0 3 4
=
B 0
0 C
B^-1=
1/2 0
0 1
C^-1=
-2 1
3/2 -1/2
A^-1=
B^-1 0
0 C^-1
=
1/2 0 0 0
0 1 0 0
0 0 -2 1
0 0 3/2 -1/2