\documentclass[border=2pt]{standalone}

% Drawing
\usepackage{tikz}
\usetikzlibrary{shapes}
%% Styles
\tikzstyle{axis} = [line width = 0.8]
\tikzstyle{node} = [draw, rectangle, rounded corners, line width=0.5]

\begin{document}
	
	\begin{tikzpicture}
		% Grid
%		\foreach \i in {-8,...,0,...,10}
%		{
%			\node at (\i,-2ex) {\i};
%			\node at (0,\i) {\i};
%		}
		
		% n=1
		%% Node
		\node[node] at (-1,0) {$n=1$};
		%% Axis
		\draw[axis] (0,0) -- (2*pi,0);
		%% Green Line
		\draw[domain=0:2*pi, samples=100,  line width = 1, green] plot (\x, {1.5*cos(deg(0.5*\x))});
		%% Valus on Axis
		\draw[thick] (0,3pt) -- (0,-3pt) node[below] {$0$};
		\draw[thick] (pi,3pt) -- (pi,-3pt) node[below] {$\frac{L}{2}$};
		\draw[thick] (2*pi,3pt) -- (2*pi,-3pt) node[below] {$L$};
		
		% n=2
		%% Node
		\node[shift={(0,-3.5)}, node] at (-1,0) {$n=2$};
		%% Axis
		\draw[shift={(0,-3.5)}, axis] (0,0) -- (2*pi,0);
		%% Blue Line
		\draw[domain=0:2*pi, samples=100, shift={(0,-3.5)}, line width = 1, blue] plot (\x, {1.5*cos(deg(\x))});
		%% Values
		\draw[shift={(0,-3.5)}, thick] (0,3pt) -- (0,-3pt) node[below] {$0$};
		\draw[shift={(0,-3.5)}, thick] (0.5*pi,3pt) -- (0.5*pi,-3pt) node[below] {$\frac{L}{4}$};
		\draw[shift={(0,-3.5)}, thick] (1.5*pi,3pt) -- (1.5*pi,-3pt) node[below] {$\frac{3L}{4}$};
		\draw[shift={(0,-3.5)}, thick] (2*pi,3pt) -- (2*pi,-3pt) node[below] {$L$};
		
		% n=3
		%% Node
		\node[shift={(0,-7)}, node] at (-1,0) {$n=3$};
		%% Axis
		\draw[shift={(0,-7)}, axis] (0,0) -- (2*pi,0);
		%% Orange Line
		\draw[domain=0:2*pi, samples=100, shift={(0,-7)}, line width = 1, orange] plot (\x, {1.5*cos(deg(1.5*\x))});
		%% Values
		\draw[shift={(0,-7)}, thick] (0,3pt) -- (0,-3pt) node[below] {$0$};
		\draw[shift={(0,-7)}, thick] (pi/3,3pt) -- (pi/3,-3pt) node[below] {$\frac{L}{6}$};
		\draw[shift={(0,-7)}, thick] (pi,3pt) -- (pi,-3pt) node[below] {$\frac{L}{2}$};
		\draw[shift={(0,-7)}, thick] (5*pi/3,3pt) -- (5*pi/3,-3pt) node[below] {$\frac{5L}{6}$};
		\draw[shift={(0,-7)}, thick] (2*pi,3pt) -- (2*pi,-3pt) node[below] {$L$};
	\end{tikzpicture}
	
\end{document}
