\documentclass[12pt]{article}
\usepackage{tikz}
\usepackage{pgf}
\usepackage{calc}
\usepackage[active,pdftex,tightpage]{preview}
\PreviewEnvironment[]{tikzpicture}


\begin{document}
       \begin{tikzpicture}[scale=1,>=stealth] 
	
	 	\def\zx{-2.6}
	 	\def\zy{1.8}
	 	\def\zzx{0.2}
	 	\def\zzy{2.3}
	 	\def\zzzx{0.8}
	 	\def\zzzy{3}

	       \draw (0,0) node[below] {$0$};
	       \draw[ultra thick,->] (0,0) -- (\zx,\zy) node[pos=0.5,above right=-3] {$\mathbf{z}$};
	       \draw (\zx,\zy) node[right=5] {$P$};

	       \draw[ultra thick,->] (0,0) -- (\zzx,\zzy) node[pos=0.5,left=-3] {$\mathbf{z_1}$};
	       \draw[ultra thick,->,xshift=3cm] (0,0) -- (\zzx,\zzy) node[pos=0.5,right=-2] {$\mathbf{z_1}$};
	       \draw (0,0) -- (3,0);
	       \draw (\zzx,\zzy) -- (3+\zzx,\zzy);

	       \draw[ultra thick,->] (0,0) -- (\zzzx,\zzzy) node[pos=0.5,right=-2] {$\mathbf{z_2}$};
	       \draw[ultra thick,->,xshift=4cm,yshift=2cm] (0,0) -- (\zzzx,\zzzy) node[pos=0.5,right=-2] {$\mathbf{z_2}$};
	       \draw (0,0) -- (4,2);
	       \draw (\zzzx,\zzzy) -- (4+\zzzx,2+\zzzy);
        \end{tikzpicture}
\end{document}

