Thông báo lỗi

Notice: Undefined offset: 1 trong counter_get_browser() (dòng 70 của /home/thayphun/viettug.net/modules/counter/counter.lib.inc).

phép đẩy nghiêng

Phép co, phép đẩy nghiêng trong tikz

\usepackage[utf8]{vietnam}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[line join=round, line cap=round]
\def\r{3}
\coordinate (S) at (0,7);
\begin{scope}[yscale=0.5]
\pgftransformxslant{0.5}
\draw[dashed, red] (0,0) circle(\r);
\draw [thick](-\r,-\r) node[below left]{$D$}
           --(\r,-\r) node[below right]{$C$}
           --(\r,\r) node[above right]{$B$};
\draw[dashed, thick] (-\r,\r) node[above left]{$A$}
                   --(-\r,-\r) (-\r,\r)--(\r,\r);
\draw [thick](S)--(-\r,-\r) (S)--(\r,-\r) (S)--(\r,\r);