I'm trying to draw this picture with tangent lines and labels but when I use sqrt(x) function(I don't know the exact function) I get a diagram like picture:

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[domain=0:6]
\draw[->] (-0.2,0) -- (6.2,0) node[right] {$x$};
\draw[->] (0,-1.2) -- (0,6.2) node[above] {$f(x)$};
\draw[color=blue] plot (\x,{1.5*sqrt(2*\x)}) node[right] {$f(x) = \sqrt x$};
\end{tikzpicture}
\end{document}
How can I get a diagram like this picture with tangent lines and notations:

\sqrtinstead ofsqrton your compiled code... but the one posted here has not that problem)... I get the same output if I change your function... – koleygr Apr 16 '18 at 07:53\draw[red] plot (\x,{sqrt(\x)}) node[right] {$f(x) =\sqrt x$};– percusse Apr 16 '18 at 08:24