用初等变换求逆矩阵!A=3 2 12 4 01 0 3 求（A-2E）的逆

(A-2E,E)=
1 2 1 1 0 0
2 2 0 0 1 0
1 0 1 0 0 1
r1-r3,r2-2r3
0 2 0 1 0 -1
0 2 -2 0 1 -2
1 0 1 0 0 1
r2-r1,r1*(1/2),r2*(-1/2)
0 1 0 1/2 0 -1/2
0 0 1 1/2 -1/2 1/2
1 0 1 0 0 1
r3-r2
0 1 0 1/2 0 -1/2
0 0 1 1/2 -1/2 1/2
1 0 0 -1/2 1/2 1/2
交换行
1 0 0 -1/2 1/2 1/2
0 1 0 1/2 0 -1/2
0 0 1 1/2 -1/2 1/2
(A-2E)^-1=
-1/2 1/2 1/2
1/2 0 -1/2
1/2 -1/2 1/2

1/2 * [-1 1 1; -1 0 1 ; 1 -1 1]