InitGraph(grDriver, grMode, '');

InitGraph(grDriver, grMode, 'EGAVGA.BGI');

  DrawPlace(@Standart, GetMin(Data), GetMax(Data), 0.1);

  SetColor(Yellow);
  SetLineStyle(DottedLn, 0, ThickWidth);
  DrawGraph(@Lagrange, GetMin(Data), GetMax(Data), 0.1);
  readln;

  SetColor(Green);
  SetLineStyle(DottedLn, 0, ThickWidth);
  DrawGraph(@Newton, GetMin(Data), GetMax(Data), 0.1);
  readln;

  SetColor(Red);
  SetLineStyle(SolidLn, 0, ThickWidth);
  DrawGraph(@Standart, GetMin(Data), GetMax(Data), 0.1);

 DrawGraph(@Lagrange, GetMin(Data), GetMax(Data), 0.01); { шаг уменьшай до 0.01 }
...
 DrawGraph(@Newton, GetMin(Data), GetMax(Data), 0.01); { здесь тоже }

procedure DrawGraph(D: PData; f: Pointer; MinX, MaxX, Step: Real);
type
  TFunction = function(x: Real): Real;
var
  p: PData;

  x, y, Inf, Sup: Real;
  xl, yt, xr, yb, i: Integer;
  Error, Define: Boolean;
begin
  if Step = 0 then Exit;
  x := MinX; Define := False;
  while x < MaxX do begin
    if not Trap then begin
      y := TFunction(f)(x);
      if not Define then begin
        Inf := y; Sup := y; Define := True; end
      else begin
        if Inf > y then Inf := y;
        if Sup < y then Sup := y;
      end;
    end;
    UnTrap;
    x := x + Step;
  end;
  if not Define then Exit;
  xl := 60; yt := 20; xr := GetMaxX - 30; yb := GetMaxY - 20;
  x := MinX;
  Error := True;
  while x < MaxX do begin
    if not Trap then begin
      y := TFunction(f)(x);
      if Error then begin
        MoveTo(xl + Round((x - MinX) * (xr - xl) / (MaxX - MinX)),
          GetMaxY - Round((y - Inf) * (yb - yt) / (Sup - Inf)) - yt);
        Error := False; end
      else
        LineTo(xl + Round((x - MinX) * (xr - xl) / (MaxX - MinX)),
          GetMaxY - Round((y - Inf) * (yb - yt) / (Sup - Inf)) - yt); end
    else
      Error := True;
    UnTrap;
    x := x + Step;
  end;

  SetColor(LightRed);
  p := D;
  while p <> nil do begin
    x := p^.x; y := p^.y;
    Circle(xl + Round((x - MinX) * (xr - xl) / (MaxX - MinX)),
      GetMaxY - Round((y - Inf) * (yb - yt) / (Sup - Inf)) - yt, 3);
    p := p^.next;
  end;
end;

  SetColor(Yellow);
  SetLineStyle(DottedLn, 0, ThickWidth);
  DrawGraph(Data, @Lagrange, GetMin(Data), GetMax(Data), 0.01);

  SetColor(Green);
  SetLineStyle(DottedLn, 0, ThickWidth);
  DrawGraph(Data, @Newton, GetMin(Data), GetMax(Data), 0.01);

  SetColor(Red);
  SetLineStyle(SolidLn, 0, ThickWidth);
  DrawGraph(nil, @Standart, GetMin(Data), GetMax(Data), 0.1); { NIL если не нужны узлы }

Program Polyn;
const
TNArraySize = 50;            { Size of vectors }
h = 0.1;
N = 3;
type
  TNvector = array[0..TNArraySize] of Real;
var
  NumPoints : integer;              { Number of data points }
  YData : TNvector;          { Data points (Y) }
  Poly : TNvector;                  { The constructed polynomial }
  k : Integer;

Function Delta(Y:TNvector):Real;     {ВОТ ЗДЕСЬ ПРОБЛЕМА}
var k:integer;
begin
     for k:=0 to N-1 do begin
     Delta:=Y[k+1]-Y[k];
     end;
end;

Function Factorial(k:Integer):Integer;
  Var m,l:Integer;
Begin;
  If k<>0 then Begin
    m:=k;
    For l:=(k-1) downto 2 do m:=m*l;
    Factorial:=m;
  End
  Else Factorial:=1;
End; {Factorial}

Function Step(k:Integer):real;
Begin
     Step:=exp(k*ln(h));
End;

Begin
for k:=0 to n do begin
   write('Y[',k,'] = ');
   readln(YData[k]);
   end;
for k:=0 to n do begin
Poly[k]:=Delta(YData[n-k])/(Factorial(k)*Step(k));  {НУ И ЗДЕСЬ СООТВЕТСТВЕННО...}
end;
end.