如题所述
|λI-A| =
λ-1 -2 -4
-2 λ+2 -2
-4 -2 λ-1
=
λ-1 -2 -λ-3
-2 λ+2 0
-4 -2 λ+3
λ-5 -4 0
= (-λ-3)(8-(λ-5)(λ+2)) =(λ+3)((λ-5)(λ+2)-8)=(λ+3)(λ-6)(λ+3)