\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{0mm}

\usepackage{pgfplots}
\pgfplotsset{compat=1.9}

\begin{document}
\begin{preview}
\begin{tikzpicture}[scale=0.5]
    \begin{axis}[
        axis x line=middle,
        axis y line=middle,
        enlarge y limits=true,
        enlarge x limits=true,
        xmin=0, xmax=2*pi, % x domain
        width=15cm, height=8cm,     % size of the image
        grid = major,
        grid style={dashed, gray!30},
        ymin=-1,      % start the diagram at this y-coordinate
        ymax= 1,      % end   the diagram at this y-coordinate
        axis background/.style={fill=white},
        ylabel=$y$,
        xlabel=$x$,
        xtick={0,1.5708,3.14159,4.7123889,6.2830},
        xticklabels={$0$,$\frac{\pi}{2}$,$\pi$,$\frac{3\pi}{2}$,$2\pi$},
        legend style={at={(0.2,0.37)}, anchor=north}
     ]
      \addplot[domain=-8:8,thick,samples=200,red]   {sin(deg(x))};
      \addplot[domain=-8:8,thick,samples=200,blue,dotted]   {cos(deg(x))};
      \legend{$\sin x$, $\cos x$}
    \end{axis}
\end{tikzpicture}
\end{preview}
\end{document}