Не правильно считает дискриминант

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TForm1 = class(TForm)
    edt1: TEdit;
    edt2: TEdit;
    edt3: TEdit;
    btn1: TButton;
    edt4: TEdit;
    edt5: TEdit;
    edt6: TEdit;
    lbl1: TLabel;
    lbl2: TLabel;
    lbl3: TLabel;
    lbl4: TLabel;
    lbl5: TLabel;
    lbl6: TLabel;
    lbl7: TLabel;
    lbl8: TLabel;
    procedure edt1Change(Sender: TObject);
    procedure edt2Change(Sender: TObject);
    procedure btn1Click(Sender: TObject);
    procedure edt4Change(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
  var
a,b,c:integer;
x1,x2,d:Double;
label m1;
 
procedure TForm1.edt1Change(Sender: TObject);
begin
  a:=strtoint (edt1.Text);
 
end;
 
procedure TForm1.edt2Change(Sender: TObject);
begin
b:=strtoint (edt2.Text);
end;
 
 
 
procedure TForm1.edt4Change(Sender: TObject);
begin
 c:=strtoint(edt2.Text);
end;
 
procedure TForm1.btn1Click(Sender: TObject);
begin
 
d:=(Sqr (b))-(4*a*c);
edt3.text:=FloatToStr(d);
if d<0 then
 
begin
 ShowMessage('ну вот и все))');
 exit;
end;
 x1:=(-b-sqrt(d))/(2*a);
 x2:=(-b+sqrt(d))/(2*a);
 edt5.text:=FloatToStr(x1);
 edt6.text:=floatToStr(x2);
end;
  end.

procedure TForm1.btn1Click(Sender: TObject);
begin
  d:=(Sqr (b))-(4*a*c);
  edt3.text:=FloatToStr(d);
  if d<0 then
...

procedure TForm1.edt2Change(Sender: TObject);
begin
b:=strtoint (edt2.Text);
end;
 
procedure TForm1.edt4Change(Sender: TObject);
begin
 c:=strtoint(edt2.Text);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
a,b,c,d:integer;
begin
a :=strtoint(Edit1.Text);
b:= strtoint(Edit2.Text);
c :=strtoint(Edit3.Text);
d :=b*b-4*a*c; //дискриминант
................................
................................ // и т.д.
end;
 
end.