\begin{tikzpicture}[scale=1.5]

\pgfplotsset{compat=1.11}

\definecolor{FireBrick}{rgb}{0.7, 0.13, 0.13}

\definecolor{NewBlue}{rgb}{0.27, 0.45, 0.76}

\tikzfading[name=arrowfading, top color=transparent!0, bottom color=transparent!95]
\tikzset{arrowfill/.style={#1,general shadow={fill=black, shadow yshift=-0.8ex, path fading=arrowfading}}}
\tikzset{arrowstyle/.style n args={3}{draw=#2,arrowfill={#3}, single arrow,minimum height=#1, single arrow,
single arrow head extend=.3cm,}}

%\NewDocumentCommand{\tikzfancyarrow}{O{2cm} O{FireBrick} O{top color=orange!20!red, bottom color=red} m}{
%\tikz[baseline=-0.5ex]\node [arrowstyle={#1}{#2}{#3}] {#4};
%}


%\node [
%  fill=blue!50, draw, 
%  single arrow,  single arrow head indent=0ex,
%  rotate=0, 
%  font=\sffamily
%] at (1,1.5) 
%{\rotatebox{0}{ \qquad}};


%\draw[color=gray!10,step=2mm,help lines] (-0.7,0) grid (72mm,58mm);
%\draw[color=gray!70,step=10mm,xshift=4mm,yshift=-1mm] (-0.5,0) grid (70mm,60mm);

\begin{axis}[
thin,
axis x line=center,
axis y line=center,
%xtick={-2,...,2},
ytick={-1,...,6},
grid = both,
minor x tick num=5,
minor y tick num=5,
%minor x tick style={line width=0pt},
major x grid style={black, line width=0.2pt},
major y grid style={black, line width=0.2pt},
minor x grid style={gray, line width=0.1pt},
%minor y tick num={5},
%minor y tick style={line width=0pt},
%yminorgrids,
%minor y grid style={black, line width=0.1pt},
xlabel style={below right},
ylabel style={above left},
minor tick length=0pt,
xmin=-2.9,
xmax=2.9,
ymin=-1.2,
style={>=latex},
yticklabel style = {font=\footnotesize,xshift=0.5ex},
xticklabel style = {font=\footnotesize,yshift=0.5ex},
% grid=both,
% grid style={line width=.1pt, draw=gray!10},
% major grid style={line width=.2pt,draw=gray!50},
ymax=5.5]
\addplot [mark=none,domain=-3.8:3.8, color=NewBlue, line width=0.75mm,smooth] {x^2};
\end{axis}

\draw[-{Triangle[scale=3,length=5,width=6]}, color=NewBlue, line width=3mm, fill=white] (2,1.5) to (0.8,1.5);
%http://latexcolor.com


\draw[-{Triangle[scale=3,length=5,width=6]}, color=NewBlue, line width=3mm] (4.8,1.5)  to (6,1.5);


\draw[draw=NewBlue, fill=white, line width=0.75mm] (-1,1.2) rectangle (0.5,1.8) node[pos=.5] {\textbf{\textcolor{black}{$-\infty$}}};


\draw[draw=NewBlue, fill=white, line width=0.75mm] (6.3,1.2) rectangle (7.8,1.8) node[pos=.5] {\textbf{\textcolor{black}{$+\infty$}}};
%\tikzfancyarrow[3cm]{} arrow

\end{tikzpicture}