im provin this little stuff:
Let $\lambda$ be double zero of $\chi_A$, where $A \neq \lambda \mathbb{I}$, i. e. $\chi_A (x) = (x - \lambda)^2$. Then there exists two lineary independent vectors $U$ and $W$, such that $AU = \lambda U$ and $AW = U + \lambda W$