% !TeX TXS-program:compile = txs:///pdflatex

\documentclass[margin=5mm]{standalone}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[x={(-135:0.4cm)},y={(0:0.5cm)},z={(90:0.45cm)},line join=bevel]
	\coordinate (O) at (0,0,0) ; \draw (O) node[below] {$O$} ;
	\coordinate (A) at (0,8,6) ; \draw (A) node[above right] {$A$} ;
	\coordinate (B) at (6,4,4) ; \draw (B) node[above] {$B$} ;
	\coordinate (C) at (2,4,0) ; \draw (C) node[below right] {$C$} ;
	\draw[thick,->,>=latex] (O)--++(6.5,0,0) node[left,font=\footnotesize] {$x$} ;
	\foreach \x in {1,2,...,6} \draw (\x,0,0) node[font=\tiny] {$\textbackslash$} ;
	\foreach \y in {1,2,...,9} \draw (0,\y,0) node[font=\tiny] {$|$} ;
	\foreach \z in {1,2,...,6} \draw (0,0,\z) node[font=\tiny] {$-$} ;
	\draw[thick,->,>=latex] (O)--++(0,9.5,0) node[below,font=\footnotesize] {$y$} ;
	\draw[thick,->,>=latex] (O)--++(0,0,7) node[left,font=\footnotesize] {$z$} ;
	\draw[semithick,fill=lightgray] (A)--(B)--(C)--cycle ;
	\draw[semithick,densely dashed] (0,0,6)--(A)--(0,8,0) ;
	\draw[semithick,densely dashed] (0,0,4)--(6,0,4)--(B)--(0,4,4)--cycle ;
	\draw[semithick,densely dashed] (6,0,4)--(6,0,0)--(6,4,0)--(B) ;
	\draw[semithick,densely dashed] (6,4,0)--(0,4,0)--(0,4,4)--(0,0,4) ;
	\draw[semithick,densely dashed] (C)--(2,0,0) ;
	\draw[semithick,->,>=latex] (O)--++(1,0,0) ;
	\draw[semithick,->,>=latex] (O)--++(0,1,0) ;
	\draw[semithick,->,>=latex] (O)--++(0,0,1) ;
\end{tikzpicture}

\end{document}