Showing that $T:V\to V$ has a cyclic vector if its eigenspaces all have dimension one.
Hints:
- It suffices to show that the minimal polynomial of $m(x)$ of $T$ is equal to the characteristic polynomial $p(x)$ of $T$, which has degree $n$.
- If $\lambda$ is an eigenvalue of $T$, then the multiplicity of $\lambda$ in $m$ is equal to the size of the largest Jordan block corresponding to $\lambda$.
- If $\lambda$ is an eigenvalue of $T$, then the algebraic multiplicity of $\lambda$, i.e. the multiplicity of $\lambda$ in $p$, is equal to the sum of the sizes of the Jordan blocks corresponding to $\lambda$.
- If $\lambda$ is an eigenvalue of $T$, then the number of Jordan blocks corresponding to $\lambda$ is equal to the geometric multiplicity of $\lambda$, which in your problem is $1$ for all eigenvalues $\lambda$.