B=
-2 -1
2 0
行列式|B|=2,代数余子式A11=0,A1=-2,A21=1,A22=-2,所以B逆=B*/|B|=
A11/|A| A21/|A|
A12/|A| A22/|A|
=
0 1/2
-1 -1