答案1
那么,很好。下面是开始绘制曲线但没有打出所有标签。
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{arrows.meta,decorations.markings}
\begin{document}
\begin{tikzpicture}[>=stealth,declare function={f(\x)=4-0.5*(\x-2)*(\x-2);}]
\draw[<->] (0,4.5) node[above left]{$v$} |- (6.5,0) node[below right] {$u$};
\draw[densely dashed] (0,2) parabola bend (2,4) ({2+2*sqrt(2)},0)
(0,2) node[left]{$Q$} (2,4) node[below]{$P$}
(0.9,0) to[out=90,in=-110] (1.4,4.5);
\draw[green!60!black,thick] (0.2,4.05) to[bend right=5]
(0.2,{f(4.7)+0.05}) -- plot[variable=\x,domain=4.7:2]
(\x+0.05,{f(\x)+0.05}) -- cycle;
\draw[purple,thick,>={Stealth[round]},postaction=decorate,
decoration={markings,
mark=at position 0.125 with {\arrow[black]{>}},
mark=at position 0.4 with {\arrow[black]{>.>}},
mark=at position 0.7 with {\arrow[black]{>}},
mark=at position 0.925 with {\arrow[black]{>.>}},
}] (0,4) --
(0,{f(4.65)}) -- plot[variable=\x,domain=4.65:2]
(\x,{f(\x)}) -- cycle;
\end{tikzpicture}
\end{document}