Short review: $ \let A \in M_{n\times m}$ If $\vec v \in \R^n$ is an [[../02 Areas/Math/Eigenvector|Eigenvector]] of $A$ with [[../02 Areas/Math/Eigenvalue|Eigenvalue]] $\lambda\in \R$, $A\vec v = \lambda \vec v$ [[../02 Areas/Math/Characteristic Polynomial|Characteristic Polynomial]]: $ \det(A-tI) =(-1)^n (t-\lambda_{1})(t-\lambda_{2})\cdots $ ]]