  \begin{pspicture}*(-10,-5)(10,5)
      \psgrid[griddots=10, gridcolor=gray, subgriddiv =0](-10,-5)(10,5)

	  \pspolygon[fillstyle = solid,fillcolor=lightgray, linestyle = dotted](-5,1)(-9,4)(5,-1)(9,-4)
	  \pspolygon(-9,4)(1,2)(9,-4)(-1,-2)

	  \psdot(-5,1)
	  \uput[d](-5,1){$A$}
	  \psdot(1,2)
	  \uput[u](1,2){$B$}
	  \psdot(-1,-2)
	  \uput[d](-1,-2){$C$}
	  \psdot(5,-1)
	  \uput[u](5,-1){$D$}

	  \psline[arrowsize=4pt 3]{->}(-5,1)(1,2)
	  \uput[u](-2,1.5){$\vec{AB}$}
	  \psline[arrowsize=4pt 3]{->}(-5,1)(-1,-2)
	  \uput[dl](-3,-0.5){$\vec{AC}$}
	  \psline[arrowsize=4pt 3]{->}(-5,1)(5,-1)
	  \uput[u](0,0){$\vec{AD}$}


	  \psdot(-9,4)
	  \uput[d](-9,4){$I$}
	  \psdot(9,-4)
	  \uput[u](9,-4){$J$}


	  \psline(-1,-2)(-9,4)
	  \psline(,2)(9,-4)



  \end{pspicture}
