const
     mash=100;
var a,b,x0,y0 : integer;
         x,y  : real;
begin
image2.Canvas.Pen.Color:=clwhite;
 image2.Canvas.Rectangle(0,0,ClientWidth,ClientHeight);
x:=StrToInt(edit1.Text);

    x0:=image2.Width div 2;
    y0:=image2.Height div 2;

image2.Canvas.Pen.Color:=clblack;
   image2.Canvas.Pen.Width:=1;

image2.Canvas.MoveTo(x0,0);
image2.Canvas.LineTo(x0,ClientHeight);
image2.Canvas.MoveTo(0,y0);
image2.Canvas.LineTo(ClientWidth,y0);


image2.Canvas.Pen.Color:=clRed;
   image2.Canvas.Pen.Width:=1;

 x:=-10;
 y:=sqr(x);
 image2.Canvas.MoveTo(trunc(x),trunc(y));
repeat
x:=x+0.1;
y:=-sqr(x) end;
image2.Canvas.LineTo(trunc(x*mash)+x0,trunc(y*mash)+y0);
until x>=10;
end;

procedure TForm1.Edit1Change(Sender: TObject);
begin
if edit1.Text='' then Button1.Enabled:=false
else
Button1.Enabled:=true;
end;

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
case key of
'0'..'9',#8:  ;
else key:= chr(0);
end;
end;
end.