# draw an upside down parabolla

I would like to draw the following figure (rotated 180 degrees--I do not know why it came out upside down) using TikZ:

It seems that this should be easy, and I have tried playing with ARC function but am coming up empty. Does someone have an idea on this?

This is what I've tried:

\def\R{\mathbb{R}}
\newcommand{\cvx}{convex}
% glossary
\begin{document}

\begin{figure}

\begin{tikzpicture}[scale=0.5]

\scriptsize

\draw (0,11.5) -- (0,0) node[below left]{$0$} -- (11,0) node[below right]{$Z$};

\node [above left] at (0,11){$\chi$};

\node [above] at (0,12){$$Consumption$$};

\node [below] at (5.5,0){$\Delta$ in $Z$};

\draw (0,0)arc(90:-90:11cm and 5.5cm);

\draw (0,5.5) node[below left]{$t^*$} -- (11,5.5);

\draw (11.2,11) -- (11.7,11) -- (11.7,5.5) -- (11.2,5.5);

\node[align=left, right] at (11.7,8.25) {Prohibitive\\Range};

\draw[fill=gray] (11,5.5)arc(0:90:11cm and 5.5cm);

\draw[fill=gray] (11,5.5) -- (0,5.5) -- (0,11);

\end{tikzpicture}

\caption{The Laffer curve}

\end{figure}

\end{document}


This is a start, if I understand your question correctly.

\documentclass[tikz,margin=2]{standalone}
\begin{document}
\begin{tikzpicture}[>=stealth]
\draw[thick] plot[smooth,samples=100,domain=-2:2] (\x,\x*\x);
\draw[<->] (-3,4) -| (2,-1);
\draw[dashed] (0,4) |- (2,0);
\end{tikzpicture}
\end{document}


• :D I absolutely (and sincerely) love your style!!! – Michael Perdue May 21 at 13:43
• @MichaelPerdue It is crazy, right :D – user156344 May 21 at 13:44
• I have one friend who comes close; but yours is truly classic :) – Michael Perdue May 21 at 13:54
• @JouleV What is difference between \x^2 and \x*\x? – minhthien_2016 May 21 at 15:17
• @JouleV I tried. Thank you very much. – minhthien_2016 May 21 at 15:23

TikZ has the parabola path construction for that purpose.

\documentclass[tikz,border=3.14mm]{standalone}
\begin{document}
\begin{tikzpicture}
\draw[stealth-stealth] (-5,0) -| (0,-5);
\draw[dashed] (-2,0) |- (0,-4);
\draw (-4,0) parabola bend (-2,-4) (0,0);
\end{tikzpicture}
\end{document}