Solution
= Solution
For a plane reflection, the $n$ direction is reversed while $n^\perp$ is fixed. Thus $L=-1$, $\alpha=1$, and $\gamma=0$, equivalently
$$
\boxed{a=\frac13,\qquad b=c=-\frac23.}
$$
= Solution
For a plane reflection, the $n$ direction is reversed while $n^\perp$ is fixed. Thus $L=-1$, $\alpha=1$, and $\gamma=0$, equivalently
$$
\boxed{a=\frac13,\qquad b=c=-\frac23.}
$$