Put texts in arbitrary place of a page

Question

I want to put some texts and some formulas in arbitrary places on several pages. For the formulas I use the package tikzpicture as the following:

\begin{tikzpicture}
\draw (5,-10)  node{
$ \left\lbrace \begin{array} \sin x>0 & 0<x<\frac{\pi}{2} \\ \sin x >0 & \frac{\pi}{2}<x<\pi \\  \sin x<0 & \pi <x<\frac{3\pi}{2} \\  \sin x<0 & \frac{3\pi}{2}<x<2\pi  \end{array} \right.  $
    };
\end{tikzpicture}

and there is no problem. But sometimes with the above way I have this problem for texts: the width of that text is bigger than the width of the page and the tikzpicture does not break the line. For example:

\begin{tikzpicture}
\draw (5,-13)  node{The proof of that theorem in not complete and  we can prove that theorem by another way that you will read it in the coming year
    };
\end{tikzpicture}

Is there a command to break lines? Is there a way to put texts in arbitrary spots of a page(with or without tikzpicture)? (Thank you very much)

Answer 1

Let me extend my comment to an answer:

\documentclass{article}
%---------------- Show page layout. Don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\noindent\begin{tikzpicture}[
node distance=0mm
                    ]
\node (n1) [left] at (\linewidth,0)
    {$\begin{cases} \sin x > 0 & 0<x<\frac{\pi}{2}      \
                    \sin x > 0 & \frac{\pi}{2}<x<\pi    \
                    \sin x < 0 & \pi <x<\frac{3\pi}{2}  \
                    \sin x < 0 & \frac{3\pi}{2}<x<2\pi  \
      \end{cases}$};
\node (n2) [below left=of n1.south east,
       text width=\linewidth, align=left,
       inner xsep=0pt] {The proof of that theorem in not complete and  we can prove that theorem by another way that you will read it in the coming year};
\end{tikzpicture}
\end{document}