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 f(x)= a*x³ + b*x² + c*x + d					

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begin
  Canvas.Brush.Color := clBlue;
  Canvas.Pen.Color := clNavy;
  Canvas.Ellipse(StrToInt(Edit1.Text)-3,StrToInt(Edit2.Text)-3,StrToInte(Edit1.Text)+3,StrToInt(Edit3.Text)+3);
end;
//und bei Create des Forms:
//------------------------
begin
  //Zeichne mit Canvas das Koordinatensystem					

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implementation
  var   xmin,xmax,ymin,ymax,k,i,z:Integer;

      begin
      Brush.Color:=clWhite;    //Hintergrundfarbe
      Pen.Color:=clBlack;      //Linienfarbe
      RectAngle(0,0,402,402);

      xmin:=1;
      xmax:=401;
      ymin:=1;
      ymax:=401;
 //Raster und Einteilung der x-Achse
      for i:=1 to z do
        begin
          Pen.Color:=clLtGray;
          moveto(xmin+k*i,ymin);
          lineto(xmin+k*i,ymax);
          Pen.Color:=clBlack;
          moveto(xmin+k*i,201-3);
          lineto(xmin+k*i,201+3);
        end;
 //Raster und Einteilung der y-Achse

      for i:=1 to z do
        begin
          Pen.Color:=clLtGray;
          moveto(xmin,ymin+k*i);
          lineto(xmax,ymin+k*i);
          Pen.Color:=clBlack;
          moveto(201-3,ymin+k*i);
          lineto(201+3,ymin+k*i);
        end;

 //Koordinatenkreuz

          moveto(xmin,201);
          lineto(xmax,201);
          moveto(201,ymin);
          lineto(201,ymax);

 //Pfeilspitze  x-Achse

          Brush.Color:=clBlack;
          Polygon([Point(390,198),Point(401,201),Point(390,204),Point(390,198)]);

 //Pfeilspitze y-Achse

          Polygon([Point(198,11),Point(201,1),Point(204,11),Point(198,11)]);
          Brush.Color:=clWhite;

 //Achsenbeschriftung

          Textout(390,205,'x');
          Textout(190,1,'y');

          if k=25 then
            begin
              Textout(222,205,'1');
              Textout(169,205,'-1');
              Textout(190,169,'1');
              Textout(186,219,'-1');
            end;
if k=10 then
            begin
              Textout(222,205,'3');
              Textout(169,205,'-3');
              Textout(190,169,'3');
              Textout(186,219,'-3');
            end;

         if k=50 then
            begin
              TextOut(245,205, '1');
              TextOut(142,205,'-1');
              TextOut(181,145, '1');
              TextOut(178,245,'-1');
            end;

         if k=5 then
            begin
              Textout(222,205,'5');
              Textout(169,205,'-5');
              Textout(190,169,'5');
              Textout(186,219,'-5');
            end;