Исправить ошибки Incompatible types и Undeclared identifier

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, TeEngine, Series, TeeProcs, Chart;
 
type
  TForm1 = class(TForm)
    btn1: TButton;
    cht1: TChart;
    lnsrsSeries1: TLineSeries;
    pnl1: TPanel;
    lbl1: TLabel;
    lbl2: TLabel;
    edt1: TEdit;
    edt2: TEdit;
    lbl3: TLabel;
    edt3: TEdit;
    btn2: TButton;
    procedure btn1Click(Sender: TObject);
    procedure btn2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
x1,x2,x,h,y,z,a,b,c,d:Real;
n,i:integer;
implementation
 
{$R *.dfm}
 
procedure TForm1.btn1Click(Sender: TObject);
begin
x:=x1;
x1:=strtoFloat(edt1.text);
h:=strtoFloat(edt3.text);
x2:=strtoFloat(edt2.text);
n:=1000;
h:=(b-a)/c;
begin
  x:=x1*(h)*x2;
  if x>=1 then y:=ln(x)
  else
  if x>-1 and 1>x then y:=1
  else
  if x<=-1 then y:=Exp(x);
  z:=x+y;
end;
d:=h*x;
pnl1.Caption:=FloatToStr(d);
end;
procedure TForm1.btn2Click(Sender: TObject);
begin
cht1.SeriesXY(x,y);
end;
end.

if (x>-1) and (1>x) then y:=1....