Решить квадратное уравнение и построить параболу

var
  a, b, c, d, x1, x2: real;
begin
   writeln('ax^2+bx+c');
   write('a=');
   readln(a);
   write('b=');
   readln(b);
   write('c=');
   readln(c);
   d :=sqr(b)-4*a*c;
   if d>=0 then
    begin
      x1:=(-b-sqrt(d))/(2*a);
      x2:=(-b+sqrt(d))/(2*a);
      writeln('x1=', x1);
      writeln('x2=', x2)
    end;
   if d<0 then writeln('Net kornej');
   readln;
end.

program EvgeniiSp;
uses GraphABC,Events;
 
type FUN = function (x: real): real;
var a,b,c: integer;
 
//------- Input_data -------//
 procedure Input_data;
  begin
   write('Ââåäèòå çíà÷åíèå a: ');
   readln(a);
   write('Ââåäèòå çíà÷åíèå b: ');
   readln(b);
   write('Ââåäèòå çíà÷åíèå c: ');
   readln(c);
  end;
  
//------- Function -------//
function f(x: real): real;
 begin
  Result:=a*sqr(x)-b*x-c;
 end;
 
// l (logical) - ëîãè÷åñêèå êîîðäèíàòû
// s (screen) - ôèçè÷åñêèå êîîðäèíàòû
procedure drawGraph(x1,x2: real; f: FUN);
 var
  xl,xl0,wl,yl,yl0,hl: real;
  xs0,ws,ys0,hs: integer;
 function LtoSx(xl: real): integer;
 begin
   Result:=round(ws/wl*(xl-xl0)+xs0);
 end;
 function LtoSy(yl: real): integer;
 begin
   Result:=round(hs/hl*(yl-yl0)+ys0);
 end;
 function StoLx(xs: integer): real;
 begin
   Result:=wl/ws*(xs-xs0)+xl0;
 end;
 var xi: integer;
     yi: array [0..1600] of real;
     min,max,y: real;
begin         // drawGraph
  xs0:=0;
  ys0:=WindowHeight-1;
  ws:=WindowWidth;
  hs:=WindowHeight-1;
 
  xl0:=x1;
  wl:=x2-x1;
 
  min:=1e300;
  max:=-1e300;
  for xi:=0 to ws do
  begin
    yi[xi]:=f(StoLx(xi+xs0));
    if yi[xi]<min then min:=yi[xi];
    if yi[xi]>max then max:=yi[xi];
  end;
  yl0:=min;
  hl:=-(max-min);
 
  MoveTo(0,LtoSy(0));
  LineTo(ws,LtoSy(0));
 
  MoveTo(LtoSx(0),0);
  LineTo(LtoSx(0),hs);
 
  SetPenColor(clBlue);
  MoveTo(xs0,LtoSy(yi[0]));
  for xi:=xs0+1 to xs0+ws do
    LineTo(xi,LtoSy(yi[xi-xs0]));
end;
 
procedure Resize;
begin
  ClearWindow;
  drawGraph(0,60,f);
  Redraw;
end;
 
begin
  Input_data;
  LockDrawing;
  SetWindowCaption('Ãðàôèê ôóíêöèè.');
  drawGraph(0,60,f);
  Redraw;
  OnResize:=Resize;
end.