Q:

Drawing a Plane in 3D space

How can I draw a plane with equation $- \sqrt{3} x+y=0 $ in space                             (with tikz)?

A:

You cannot simply use rectangle, which will not produce the expected output. But you can draw the plane "manually" like so:

\documentclass{article}

\usepackage{tikz}
\usepackage{tikz-3dplot}

\begin{document}

\tdplotsetmaincoords{70}{110}
\begin{tikzpicture}[scale=3,tdplot_main_coords]
    \draw[thick,->] (0,0,0) -- (1,0,0) node[anchor=north east]{$x$};
    \def\x{.5}
    \draw[thin] (0,0,0) -- ({1.2*\x},{sqrt(3)*1.2*\x},0) node[below] {$y=\sqrt{3}x$};
    \filldraw[
        draw=red,%
        fill=red!20,%
    ]          (0,0,0)
            -- (\x,{sqrt(3)*\x},0)
            -- (\x,{sqrt(3)*\x},1)
            -- (0,0,1)
            -- cycle;
    \draw[thick,->] (0,0,0) -- (0,1,0) node[anchor=north west]{$y$};
    \draw[thick,->] (0,0,0) -- (0,0,1) node[anchor=south]{$z$};
\end{tikzpicture}

\end{document}

