Question 122
For which values of parameter $a$ the system of equations
$$
\begin{cases} x + y + z = 0 \\ (xy + yz) + a xz = 0 \end{cases} \text{ has a unique solution?}
$$
$$
\begin{cases} x + y + z = 0 \\ (xy + yz) + a xz = 0 \end{cases} \text{ has a unique solution?}
$$