Solution
= Solution
The direction <vectors> are $v=(-1,-1,1)$ and $w=(1,1,2)$. Their <scalar product> is $v\cdot w=-1-1+2=0$. Both are nonzero, so the lines are perpendicular:
$$
\boxed{\theta=\frac\pi2=90^\circ}.
$$
= Solution
The direction <vectors> are $v=(-1,-1,1)$ and $w=(1,1,2)$. Their <scalar product> is $v\cdot w=-1-1+2=0$. Both are nonzero, so the lines are perpendicular:
$$
\boxed{\theta=\frac\pi2=90^\circ}.
$$