题目不对,简单举个反例:
A=
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 2
B=
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 3
A-3B=
-2 0 0 0
0 -2 0 0
0 0 -2 0
0 0 0 -7
|A-3B| = 56
A=
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 2
B=
-1 0 0 0
0 -1 0 0
0 0 1 0
0 0 0 3
A-3B=
4 0 0 0
0 4 0 0
0 0 -2 0
0 0 0 -7
|A-3B| = 224