I read that a Matrix $A$ has the eigenvalue $0$ if and only if $\ker(A) \neq \{0\}$.
Why so?
Edit Okay actually I figured it out myself. If $0$ is an eigenvalue of a matrix $A$ then $\det(A)=0$ and then $A$ is not invertible, therefore the rows are not linearly independent: $\ker(A) \neq0$.