(-1,1,2)=A
( 1,0,4)
( 2,-1,-1)
E+A=
(0,1,2)
(1,1,4)
(2,-1,0)
通过初等行变换得
(E+A)^(-1)=
(2,-1,1)
(4,-2,1)
(-1.5,1,-0.5)