Program Pascal Regula falsi

program regulafalsi;
uses crt;
label ulang;
var
x1,x2,x3,y1,y2,y3 : real;
i : integer;
Ab :char;
data1 : real;
begin

    ulang:
    clrscr;
    writeln('Tentukan nilai akar dari persamaan f(x)=x^3+x^2-3x-3=0 dengan Regula Falsi');
    write('Masukan nilai x1 = ');readln(x1);
    y1 := x1 * x1 * x1 + x1 * x1 - 3 * x1 - 3;
    writeln(' Nilai f(x1)= ',y1:0:4);
    repeat
    begin
      write( 'Masukan nilai x2 = ' ); readln(x2);
      y2 := x2 * x2 * x2 + x2 * x2 - 3 * x2 - 3;
      write(' Nilai f(x2)= ',y2:0:4);
    end;
    if (y1*y2)<0 then
      Writeln(' Syarat Nilai Ok')
    else
      Writeln(' Nilai X2 Belum Sesuai');
    until ( y1 * y2 ) <0;
    writeln;
    writeln('Penyelesaian persamaan karekteristik dengan metoda regula falsi');
    writeln('----------------------------------------------------------------------');
    writeln(' n          x                    f(x)               error ');
    writeln('----------------------------------------------------------------------');
    repeat
    begin
      i:= i + 1; x3 := ( x2-( y2 / ( y2 - y1))*(x2-x1));
      y3 := x3 * x3 * x3 + x3 * x3 - 3 * x3 - 3;
    if i<10 then
      writeln(' ',i,' : ',x3,' : ',y3,' : ',abs(y3),' : ')
    else
      writeln(i,' : ',x3,' : ',y3,' : ',abs(y3),' : ');
    if ( y1 * y3 ) <0 then
      begin
      x2 := x3 ; y2 := y3 ;
      end
    else
    begin
      x1 := x3 ; y1 := y3;
    end;
    end;
    until abs( y3 ) < 1E-07;
    writeln('----------------------------------------------------------------------');
    writeln('Akar persamaannya= ',x3);
    writeln('Errornya=' ,abs( y3 ));
    writeln('----------------------------------------------------------------------');
    write('Apakah anda ingin mengulangi (y/t): ');
    readln(ab);
    if (ab='y') or (ab='Y') then
      begin
      goto ulang;
      end
    else
end.