Q70. $\quad x + ( \sqrt { 2 } \sin \alpha ) y + ( \sqrt { 2 } \cos \alpha ) z = 0$\\
If the system of equations $x + ( \cos \alpha ) y + ( \sin \alpha ) z = 0 \quad$ has a non-trivial solution, then $\alpha \in \left( 0 , \frac { \pi } { 2 } \right)$ is
$$x + ( \sin \alpha ) y - ( \cos \alpha ) z = 0$$
equal to :\\
(1) $\frac { 11 \pi } { 24 }$\\
(2) $\frac { 5 \pi } { 24 }$\\
(3) $\frac { 7 \pi } { 24 }$\\
(4) $\frac { 3 \pi } { 4 }$