\documentclass[10pt,a4paper]{article}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage [frenchb]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}



\usepackage{pstricks,pstricks-add,pst-plot}
\definecolor{chamois}{RGB}{255,230,179}
\definecolor{brun}{RGB}{222,184,135}
\definecolor{brunfonce}{RGB}{84,31,0}
\definecolor{bleu}{RGB}{0,85,102}

\begin{document}
\psset{algebraic=true,%
xunit=0.7cm, 
yunit=0.2cm, 
linewidth=0.3pt,
plotpoints=300}
\begin{pspicture}(-1,-1)(11,20) 
\pscustom[fillstyle=solid,fillcolor=chamois,linecolor=brun]{%
	\psplot{0}{3}{(20*x+10)*2.718^(-0.5*x)}
	\psline(3,0)(0,0)}
\psaxes[Dx=1,Dy=2,xticksize=3pt ,yticksize=-3pt  ]{->}(0,0)(0,0)(11,20)
\psline[linestyle=dotted](4.67,0)(4.67,10)
\psplot[linecolor=brunfonce]{0}{10}{(20*x+10)*2.718^(-0.5*x)}
\psplot[linecolor=bleu]{0}{9}{10}
\uput[140](4.8,0){\textcolor{red}{$\alpha$}}
\uput[0](9,10){\textcolor{red}{$y=10$}}
\psdots[linecolor=red,dotscale=1.5,dotstyle=o](0,10)(4.67,10)
\end{pspicture}




\end{document}