Известны координаты вершин треугольника

Program Kentaw;
uses crt;
var
 x1,y1,x2,y2,x3,y3,x4,y4,AB,BC,AC,OC,OB,OA:real;
 p_ABC, p_AOB, p_BOC, p_AOC,S_ABC,S_AOB,S_BOC,S_AOC:Real;
begin
  clrscr;
  Writeln('Vvodite vershini treuqolnika najimaya <Enter>');
  Readln(x1);
  Readln(y1);
  Readln(x2);
  Readln(y2);
  Readln(x3);
  Readln(y3);
  Writeln('Vvodite koordinayi zadannoqo tochka');
  Readln(x4);
  Readln(y4); 
  AB:=SQRT(SQR(x2-x1)+SQR(y2-y1));
  BC:=SQRT(SQR(x3-x2)+SQR(y3-y2));
  AC:=SQRT(SQR(x3-x1)+SQR(y3-y1));
  OA:=SQRT(SQR(x4-x1)+SQR(y4-y1)); 
  OB:=SQRT(SQR(x4-x2)+SQR(y4-y2));
  OC:=SQRT(SQR(x4-x3)+SQR(y4-y3)); 
  p_ABC:=(AB+BC+AC)/2;
  S_ABC:=sqrt(p_ABC*(p_ABC-AB)*(p_ABC-AC)*(p_ABC-BC));  
  p_AOB:=(AB+OB+OA)/2;
  S_AOB:=sqrt(p_AOB*(p_AOB-AB)*(p_AOB-OB)*(p_AOB-OA));   
  p_BOC:=(OB+BC+OC)/2;
  S_BOC:=sqrt(p_BOC*(p_BOC-OB)*(p_BOC-BC)*(p_BOC-OC));  
  p_AOC:=(OA+OC+AC)/2;
  S_AOC:=sqrt(p_AOC*(p_AOC-OA)*(p_AOC-OC)*(p_AOC-AC));
  if abs(S_AOB+S_BOC+S_AOC-S_ABC)<0.00000001 then writeln('DA!') else writeln('NET!');
  readln 
 
end.