\documentclass[10pt]{article}
\usepackage{pgf,tikz,pgfplots}
\pgfplotsset{compat=1.15}
\usepackage{mathrsfs}
\usetikzlibrary{arrows}
\pagestyle{empty}
\newcommand{\degre}{\ensuremath{^\circ}}
\begin{document}
\definecolor{qqwuqq}{rgb}{0,0.39215686274509803,0}
\definecolor{ududff}{rgb}{0.30196078431372547,0.30196078431372547,1}
\definecolor{xdxdff}{rgb}{0.49019607843137253,0.49019607843137253,1}
\definecolor{uuuuuu}{rgb}{0.26666666666666666,0.26666666666666666,0.26666666666666666}
\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1cm,y=1cm]
\begin{axis}[
x=1cm,y=1cm,
axis lines=middle,
ymajorgrids=true,
xmajorgrids=true,
xmin=-1.3544263878097484,
xmax=9.691411951745668,
ymin=-3.214189806288097,
ymax=6.1825790285103785,
xtick={-1,-0.5,...,9.5},
ytick={-3,-2.5,...,6},]
\clip(-1.3544263878097484,-3.214189806288097) rectangle (9.691411951745668,6.1825790285103785);
\draw[line width=2pt,color=qqwuqq,fill=qqwuqq,fill opacity=0.10000000149011612] (8,0.20699436025945198) -- (7.793005639740548,0.206994360259452) -- (7.793005639740548,0) -- (8,0) -- cycle; 
\draw [line width=2pt] (0,0)-- (8,0);
\draw [line width=2pt] (8,0)-- (8,4);
\draw [->,line width=2pt] (0,0) -- (8,4);
\begin{scriptsize}
\draw [fill=uuuuuu] (0,0) circle (2pt);
\draw[color=uuuuuu] (0.07997134709718273,0.18640618429058298) node {$A$};
\draw [fill=xdxdff] (8,0) circle (2.5pt);
\draw[color=xdxdff] (8.081373677870541,0.2059217997314936) node {$B$};
\draw[color=black] (4.031883473881585,-0.03802339327988945) node {$f$};
\draw [fill=ududff] (8,4) circle (2.5pt);
\draw[color=ududff] (8.081373677870541,4.206622965118176) node {$C$};
\draw[color=black] (8.188709562795548,2.1184521129407368) node {$g$};
\draw[color=qqwuqq] (8.315561063161468,0.18640618429058298) node {$\alpha = 90\textrm{\degre}$};
\draw[color=black] (4.012367858440674,2.157483343822558) node {$u$};
\end{scriptsize}
\end{axis}
\end{tikzpicture}
\end{document}