bai 13

var x, y, z:longint;

      P:real;

bai 14

var a:qword;

begin

 writeln('nhap so nguyen a');

 readln(a);

 if a mod 9=0 then writeln('so nay chia het cho 9 va 3')

  else if a mod 3=0 then writeln('so nay chi chia het cho 3')

   else writeln('so nay khong chia het cho 3 va 9');

 readln;

end.

bai 15

var a,b,c:qword;

       s:real;

begin

 writeln('nhap lan luot 3 so a, b, c');

 readln(a,b,c);

 if (a+b>c)and(a+c>b)and(b+c>a) then begin

  s:=(a+b+c)/2;

  s:=sqrt(p*(p-a)*(p-b)*(p-c));

  writeln('day la 3 canh tam giac co chu vi la :',s);

 end else write('day khong phai 3 canh cua tam giac');

 readln;

end.

Câu 13: 

var x,y,z:longint; P:real;

Câu 14: 

uses crt;
var a:longint; 
begin
clrscr;
   write('Nhap so nguyen a: ');readln(a);
   if (a mod 3=0)and(a mod 9=0) then 
      writeln('a chia het cho 3 va 9') else   
      writeln('a khong chia het cho 3 va 9');
readln
end.

Câu 15:

 uses crt;
var a,b,c:longint; 
begin
clrscr;
   write('Nhap so nguyen a: ');readln(a);
   write('Nhap so nguyen b: ');readln(b);
   write('Nhap so nguyen c: ');readln(c);
   if (a+b>c)and(a+c>b)and(b+c>a) then 
      begin
         writeln('Day la do dai 3 canh cua tam giac');
         writeln('Chu vi: ',a+b+c);
      end else writeln('Day khong la do dai 3 canh cua tam giac');
readln
end.