\begin{pspicture}(-0.3,-0.4)(5.6,2.3) \psgrid(0,0)(5.6,2.3) \psline[linecolor=blue, linewidth=0.5pt]{->}(0,0)(4.7,0) \psline[linecolor=blue, linewidth=0.5pt]{->}(0,0)(0.7,2) \psline[linecolor=red, linewidth=0.5pt, linestyle=dashed](0.7,2)(5.4,2) \psline[linecolor=red, linewidth=0.5pt, linestyle=dashed](4.7,0)(5.4,2) %\rput[c](0.25,1.15){\color{blue}\tiny{+}} \rput[c](2.5,-0.25){$\vec{a}$} \rput[c](0.1,1.1){$\vec{b}$} %\psline[linecolor=red, linewidth=0.5pt]{->}(2.1,1.1)(0.3,0.1) \rput[c](0.55,0.4){\color{lila}$\alpha$} \psarc[linewidth=0.5pt, linecolor=lila]{->}{1}{0}{70} \end{pspicture}