What is the transformation matrix for a reflection across the line y=3xy = \sqrt{3}xy=3x?
\begin{pmatrix} -0.5 & 0.866 \ 0.866 & 0.5 \end{pmatrix}
\begin{pmatrix} 0.5 & 0.866 \ 0.866 & -0.5 \end{pmatrix}
\begin{pmatrix} 1 & 0 \ 0 & -1 \end{pmatrix}
\begin{pmatrix} -1 & 0 \ 0 & 1 \end{pmatrix}