解: 因为 AB=A+B
所以 (A-E)B=A
(A-E,A)=
1 1 0 2 1 0
0 1 1 0 2 1
0 0 1 0 0 2
r2-r3,r1-r2
1 0 0 2 -1 1
0 1 0 0 2 -1
0 0 1 0 0 2
所以 B=
2 -1 1
0 2 -1
0 0 2
解: 因为 AB=A+B
所以 (A-E)B=A
(A-E,A)=
1 1 0 2 1 0
0 1 1 0 2 1
0 0 1 0 0 2
r2-r3,r1-r2
1 0 0 2 -1 1
0 1 0 0 2 -1
0 0 1 0 0 2
所以 B=
2 -1 1
0 2 -1
0 0 2