答案1
\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}
% 7/90*180=14
% -1/7*180=-25.71428571
% 6/7*180=154.2857143
\draw
[thick,color=black,domain=-25.71428571:154.2857143,samples=200,smooth]
plot (xy polar cs:angle=\x,
radius=
{1/sqrt(1-0.9800139176438553*cos(\x-14)*cos(\x-14))});
\end{tikzpicture}
\end{document}
TikZcos
默认sin
使用度数。