Given A=(1234)A = \begin{pmatrix} 1 & 2 \\ 3 & 4 \end{pmatrix}A=(1324), what is the characteristic polynomial p(λ)=det(A−λI)p(\lambda) = \det(A - \lambda I)p(λ)=det(A−λI)?
λ2−5λ−2\lambda^2 - 5\lambda - 2λ2−5λ−2
λ2+5λ+2\lambda^2 + 5\lambda + 2λ2+5λ+2
λ2−5λ+2\lambda^2 - 5\lambda + 2λ2−5λ+2
λ2+5λ−2\lambda^2 + 5\lambda - 2λ2+5λ−2