# dashed lines in intersections and graph

I was trying to repeat this graph, but only a part of it. And my goal is to make the TP curve more downward at the end. In addition, I find difficult to make the dashed lines there. Is there a way to fix it?

Some equation that might work:

TP: Q=21x+9x^2-x^3 AP: Q=21+9x-x^2 MP: 21+18x-3x^2

Graph wanted:

Code:

\documentclass{standalone}
\usepackage[english,greek]{babel}
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{tikz}
\usepackage{tkz-tab}
\usepackage{cancel}
\usepackage{forest}
\usepackage{caption}
\usepackage{latexsym}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{pst-node}
\def\obj#1{\makebox[1cm]{\strut#1}}
\usepackage{pdflscape}
\usepackage{paralist}
\usepackage{pst-tree,array}
\usepackage{enumerate}
\usepackage{graphicx}
\usepackage{subcaption}
\usepackage{rotating}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{chngcntr}
\usepackage[framemethod=tikz]{mdframed}
\usepackage{wrapfig}
\usepackage{color}
\usepackage[explicit]{titlesec}
\usepackage{appendix}
\usepackage{etoolbox}
\usepackage{type1cm}
\usepackage{lettrine}
\usepackage[stable]{footmisc}
\usepackage{multicol}
\usepackage{chngcntr}
\usepackage{url}
\usepackage{marvosym}
\usepackage{tcolorbox}
\usepackage{hyperref}
\tcbuselibrary{theorems}
\usepackage{tkz-euclide}
\usetikzlibrary{shapes.geometric}
\usepackage{tkz-fct} \usetkzobj{all}
\usetikzlibrary{calc,decorations.pathreplacing}
\usetikzlibrary{decorations.markings}
\usepackage{pgfplots}
\usepackage{verbatim}
\usepackage{smartdiagram}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{intersections}

\begin{document}

\begin{tikzpicture}[scale=.8,>=latex,font=\footnotesize,domain=0:7]
\begin{scope}
\begin{scope}[yscale=-1,rotate=-90]
\draw[Red,thick,yscale=.25] plot (\x,{.2*\x^3-1.8*\x^2+6*\x})
node[above right]{$TP$};
\end{scope}
\begin{scope}[domain=1:6, rotate=0]
\draw[Green,thick,yscale=.6,name path global=MP] plot (\x,{-.6*\x^2+3.6*\x-1.5})
node[right]{$MP$};
\draw[Blue, thick,yscale=.6,name path global=AP] plot (\x,{-.2*\x^2+1.8*\x-.1})
node[right]{$AP$};
\end{scope}
\draw[very thick, <->](0,8)node[left]{$Q$}--(0,0)--(8,0)node[below]{$L$};
\end{scope}
\draw[name intersections={of=AP and MP, by=mypoint},dashed](mypoint)--(mypoint|-0,0);

\end{tikzpicture}
\end{document}
• You should remove the outmost scope, it has unnecessary [y shift=20cm]. Are the functions you used for TP, MP, and AP the same as the one used to get the desired figure? Or did you create your own functions to draw those curves? Your problem is closer to creating the correct form of the three functions than to TikZ. Jul 9 '16 at 17:01
• How can the intersection move where AP=MP? Also, how can the TP line become like the one on the figure above (I mean at the end of it)?
– Y_gr
Jul 10 '16 at 21:03
– cfr
Jul 10 '16 at 21:33
• It seems that you haven't tikz problem but math problem: find appropriate function for your graph. From sketch follows that MP paths is derivative of TP paths and APmax lie on intersection of MP and AP. So, probably you miss the right forum for your problem ... Jul 17 '16 at 16:18

• the useful lines are buried among many unuseful ones
• (maybe for this reason) the connection between math and tikz has been lost from sight.

Anyway, after cleaning up your code, I changed the definition of the TP function into the correct one, added the dashed line, and added the label making the connection between the maximal value and the zero of MP.

The code

\documentclass[11pt, margin=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{intersections}

\begin{document}

\begin{tikzpicture}[scale=1, domain=0:7, every node/.style={scale=.8},
points to/.style={thin, arrows={->[length=.5ex]},
black!40, shorten >=5pt, shorten <=5pt},
y={(0, .3 cm)}, samples=150]
\draw[very thin, <->] (0, 20) node[left] {$Q$} -- (0, 0)
-- (8, 0) node[below] {$L$};

\draw[red, thick, name path=TP] plot (\x, {-.2*\x^3+1.8*\x^2})
node[right]{$TP$};
\draw[green!50!black, thick, name path=MP]
plot (\x, {-.6*\x^2+3.6*\x}) node[right]{$MP$};
\draw[blue, thick, name path=AP]
plot (\x, {-.2*\x^2+1.8*\x-.01}) node[right]{$AP$};  % needed for the point $I$

\draw[name intersections={of=AP and MP, by=I}, dashed, very thin]
(I) -- (I|-0, 0);
\draw[dashed, very thin] (6, 0) node (MP=0){}
-- ++(0, {-.2*6^3+1.8*6^2}) node (TPmax) {};
\path (7, 10) node[right] (label) {$TP$ max when $MP=0$}
edge[out=-90, in=15, points to] (MP=0) edge[out=85, in=-70, points to] (TPmax);
\end{tikzpicture}
\end{document}