2. |A| =
|k 1 1 1|
|1 k 1 1|
|1 1 k 1|
|1 1 1 k|
|A| =
|k+3 1 1 1|
|k+3 k 1 1|
|k+3 1 k 1|
|k+3 1 1 k|
|A| =
|k+3 1 1 1|
|0 k-1 0 0|
|0 0 k-1 0|
|0 0 0 k-1|
|A| =(k+3)(k-1)^3 = 0
则 k = -3 或 k = 1