$$( D ^ { 2 } - 5 D + 4 ) y = 0$$
$\left\{\begin{matrix}\\y=0\text{, }&\text{unconditionally}\\y\in \mathrm{C}\text{, }&D=1\text{ or }D=4\end{matrix}\right.$
$\left\{\begin{matrix}\\y=0\text{, }&\text{unconditionally}\\y\in \mathrm{R}\text{, }&D=1\text{ or }D=4\end{matrix}\right.$
$\left\{\begin{matrix}\\D=1\text{; }D=4\text{, }&\text{unconditionally}\\D\in \mathrm{C}\text{, }&y=0\end{matrix}\right.$
$\left\{\begin{matrix}\\D=1\text{; }D=4\text{, }&\text{unconditionally}\\D\in \mathrm{R}\text{, }&y=0\end{matrix}\right.$
