The locus represented by $x y+y z=0$ is

The plane $2 x-3 y+6 z-11=0$ makes an angle $\sin ^{-1}(\alpha)$ with $X$-axis, the value of $\alpha$ is equal to

The perpendicular distance of the point $P(6,7,8)$ from $X Y$-plane is

Reflexion of the point $(\alpha, \beta, \gamma)$ in $X Y$-plane is