\input{preamble-standalone.ltx}
\begin{document}

% Ex. No. 18 (Section  7.2 : Tangente avec \tkzname{xstep} et \tkzname{ystep} différents de 1)

\begin{tikzpicture}[xscale=1.5]
 \tikzset{tan style/.style={-}}
 \tkzInit[xmin=0,xmax=800,xstep=100,
          ymin=0,ymax=1800,ystep=400]
 \tkzGrid[color=brown,sub,subxstep=50,subystep=200](0,0)(800,1800)
 \tkzAxeXY
 \tkzFct[color=red,samples=100,domain = 0:800]%
    {(1./90000)*\x*\x*\x-(1./100)*\x*\x+(113./36)*\x}
 \tkzDrawTangentLine[color=blue,kr=300,kl=450,coord](450)
 \tkzText[draw, color    = black,%
           fill     = brown!50, opacity  = 0.8](300,1200)%
 {$f(x)=\dfrac{1}{90000}x^3 -\dfrac{1}{{100}}x^2 +\dfrac{113}{36}x$}
\end{tikzpicture}

\end{document}
