end.
Bài I.4:
program bai4_ld;
uses crt;
var n:integer;
begin
clrscr;
write('Nhap n='); readln(n);
if n mod 2=0 then
 writeln('So chan nx2 =',2*n)
else
 writeln('So le n=',n);
readln;
end.

Bài I.5:
program bai5_ld;
uses crt;
var n:integer;
begin
clrscr;
write('Nhap n='); readln(n);
if n >5 then
 writeln('So > 5, n+2 =',n+2)
else
 writeln('So <5, =',0);
readln;
end.

Bài 6:
program bai6_ld;
uses crt;
var i,n,s:integer;
begin
clrscr;
write('Nhap n='); readln(n);
s:=1;
for i:=1 to n do
 s:=s*i;
writeln('S=',s);
readln;
end.

Bài 7:
program bai7_ld;
uses crt;
var i,n,s:integer;
begin
clrscr;
write('Nhap n='); readln(n);
s:=1; i:=1;
while i<=n do
  begin 
 s:=s*i;
 i:=i+2;
  end;
writeln('S=',s);
readln;
end.

Bài 8:
program bai8_ld;
uses crt;
var i,n,s:integer;
begin
clrscr;
write('Nhap n='); readln(n);
s:=0; i:=1;
while i<=2*n+1 do
  begin 
 s:=s+i;
 i:=i+2;
  end;
writeln('S=',s);
readln;
end.

Bài 9:
program bai9_ld;
uses crt;
var i,n,s,dau:integer;
begin
clrscr;
write('Nhap n='); readln(n);
s:=0; dau:=1;
for i:=1 to n do
  begin 
    s:=s+i*dau;
    dau:=-dau
  end;
writeln('S=',s);
readln;
end.

Bài 10:
program bai10_ld;
uses crt;
var i,n,s,d:integer;
begin
clrscr;
write('Nhap n='); readln(n);
s:=0; d:=1;
for i:=1 to n do
  begin
    d:=d*i;
  s:=s+d;
  end;
writeln('S=',s);
readln;
end.

Bài 11:
program bai11_ld;
uses crt;
var i,n,s:integer;
begin
clrscr;
write('Nhap n='); readln(n);
s:=0;
for i:=1 to n do
  s:=s+i*i;
writeln('S=',s);
readln;
end.
Bài 12:
program bai11_ld;
uses crt;
var i,n:integer;
 s:real;
begin
clrscr;
write('Nhap n='); readln(n);
s:=0;
for i:=1 to n do
  s:=s+1/i;
writeln('S=',s:4:2);
readln;
end.

Bài 13:
{program bai_i13;
uses crt;
var i,n,tmp:integer;
    s:real;
begin
clrscr;
  write('Nhap n='); readln(n);
  s:=0; tmp:=1;
  for i:=1 to n do
   begin
     s:=s+1/tmp;
     tmp:=tmp+i;
   end;
  write('Tong s=', s:4:1);
readln;
end.
Bài I.14

program bai_i14;
uses crt;
var x,y:integer;
    p:real;
begin
clrscr;
  write('Nhap x,y='); readln(x,y);
  if x>0 then
    begin
       p:=exp(y*ln(x));
       write('Tong s=',p);
    end;
readln;
end.
Bài I.15
program bai_i15;
uses crt;
var i,n,tmp,s:integer;
begin
clrscr;
  write('Nhap n='); readln(n);
  s:=0; tmp:=0;
  for i:=1 to n do
   begin
     tmp:=tmp+i;
     s:=s+tmp;
   end;
  write('Tong s=', s);
readln;
end.
Bài I.16
program bai_i16;
uses crt;
var n,s:integer;
begin
clrscr;
  write('Nhap n='); readln(n);
  s:=abs(n);
  write('Tong s=',s);
readln;
end.
Bài I.17
program bai_i17;
uses crt;
var n:longint;
    max:byte;
begin
clrscr;
  write('Nhap n='); readln(n);
  max:=n mod 10;
  while n div 10<>0 do
  begin
   if(n mod 10)>max then
     max:=n mod 10;
   n:=n div 10;
  end;
  write('Max=',max);
readln;
end.
Bài I.18
program bai_i18;
uses crt;
var i,n,d:integer;
begin
clrscr;
  write('nhap n='); readln(n);
  d:=0;
  for i:= 1 to n do
   if (n mod i=0) and (i mod 2=0) then
      d:=d+1;
  writeln('So uoc so',d);
readln;
end.
Bài I.19
program bai_i19;
uses crt;
var n,k,m:longint;
begin
clrscr;
  write('Nhap n=');
  readln(n);
  k:=0;m:=n;
  while m div 10 <> 0 do
   begin
    k:=k+1;
    m:=m div 10;
   end;
   k:=round(exp(k*ln(10)));
   writeln('k=',k);
  writeln('So dau tien cua so n la: ',n div k);
readln;
end.
Bài I.20

program bai_i20;
uses crt;
var a,b,uscln:integer;
begin
clrscr;
  write('Nhap a,b='); readln(a,b);
  while a<>b do
   if a> b then
     a:=a-b
   else
     b:=b-a;
  uscln:=a;
  write('USCLN=',uscln);
readln;
end.
Bài I.21
program bai_i21;
uses crt;
var a,b,uscln,bscnn,m,n:integer;
begin
clrscr;
  write('Nhap a,b='); readln(a,b);
  m:=a; n:=b;
  while a<>b do
   if a> b then
     a:=a-b
   else
     b:=b-a;
  uscln:=a;
  bscnn:=round((m*n)/uscln);
  write('BSCNN=',bscnn);
readln;
end.
Bài I.22
program bai_i22;
uses  crt;
var x,i,d:integer;
begin
clrscr;
 write('Nhap x='); readln(x);
 d:=0;
 for i:=2 to x do
   if x mod i=0 then
      d:=d+1;
 if d=1 then  writeln(x,' la so nguyen to')
 else writeln(x,' ko phai la so nguyen to');
readln;
end.
Bài I.23

program bai_i23;
uses crt;
var x:integer;
begin
clrscr;
 write('Nhap x='); readln(x);
 if sqr(trunc(sqrt(x)))=x then {trunc(): cat lay phan nguyen
    write(x,' la so chinh phuong')
 else
   write(x,' khong phai la so chinh phuong');
 readln;
end.
Bài I.24
program bai_i24;
uses crt;
var x,i,s,j:integer;
begin
clrscr;
  write('Nhap x='); readln(x);
  s:=0;
  for i:=2 to x do
   if x mod i=0 then
     s:=s+i;
   if s<x then
     writeln(x,' la so hoan thien')
   else
     writeln(x,' khong phai la so hoan thien');
readln;
end.
Bài I.25
program bai_i25;
uses crt;
var i,n:integer;
 s:real;
begin
clrscr;
 write('Nhap n='); readln(n);
 s:=0;
 for i:=1 to n do
  s:=s+exp(i*ln(i));
 write('Tong s=',s:4:2);
readln;
end.
Bài I.26
program bai_i26;
uses crt;
var i,n:integer;
 s:real;
begin
clrscr;
 write('Nhap n='); readln(n);
 s:=0;
 for i:=1 to n do
  s:=s+i/(i+1);
 write('Tong s=',s:4:2);
readln;
end.
Bài I.27
program bai_i27;
uses crt;
var i,n,gt:integer;
 s:real;
begin
clrscr;
 write('Nhap n='); readln(n);
 s:=0;gt:=1;
 for i:=1 to n do
   begin
  gt:=gt*i;
    s:=s+1/gt;
   end;
 write('Tong s=',s:4:2);
readln;
end.
Bài I.28
program bai_i28;
uses crt;
var i,n,t,m:integer;
 s:real;
begin
clrscr;
 write('Nhap n='); readln(n);
 s:=0;t:=0; m:=1;
 for i:=1 to n do
   begin
  t:=t+i;
  m:=m*i;
    s:=s+t/m;
   end;
 write('Tong s=',s:4:2);
readln;
end.
Bài I.29
program bai_i29;
uses crt;
var a,b,c,dt,x1,x2:real;
begin
clrscr;
 write('Nhap a,b,c='); readln(a,b,c);
 if a=0 then
  if b= 0 then
   if c=0 then write('PT_vsn')
   else write('Pt_vn')
  else write('Pt co nghiem=',-c/b:4:2)
 else
  begin
  dt:=b*b-4*a*c;
  if dt<0 then write('Pt_Vn')
  else
   if dt = 0 then write('Pt_co nghiem',-b/(2*a):4:2)
   else
    begin
     x1:=(-b-sqrt(dt))/(2*a);
     x2:=(-b+sqrt(dt))/(2*a);
     writeln('Pt co hai nghiem:');
     writeln('x1=',x1:4:2);
     writeln('x2=',x2:4:2);
    end;
    end;
readln;
end.
Bài I.30
program bai_i30;
uses crt;
var a,b,c,dt,x1,x2,x,x3:real;
begin
clrscr;
 write('Nhap a,b,c='); readln(a,b,c);
 if a=0 then
  if b= 0 then
   if c=0 then write('PT_vsn')
   else write('Pt_vn')
  else
   begin
    x:=-c/b;
    if x>=0 then
      begin
     writeln('Nghiem x1=',sqrt(x));
     writeln('Nghiem x2=',-sqrt(x));
      end
    else writeln('PT_vn');
   end
 else
  begin
  dt:=b*b-4*a*c;
  if dt<0 then write('Pt_Vn')
  else
   if dt = 0 then
    begin
     x:=-c/b;
     if x>=0 then
      begin
       writeln('Nghiem x1=',sqrt(x));
       writeln('Nghiem x2=',-sqrt(x));
      end
     else writeln('PT_vn');
    end
   else
    begin
     x1:=(-b-sqrt(dt))/(2*a);
     x2:=(-b+sqrt(dt))/(2*a);
     if (x1>=0) and (x2>=0) then
     begin
      writeln('Nghiem x1=',sqrt(x1));
      writeln('Nghiem x2=',-sqrt(x1));
      writeln('Nghiem x3=',sqrt(x2));
      writeln('Nghiem x4=',-sqrt(x2));
     end
     else
      begin
      if x1>0 then
       begin
        writeln('Nghiem x1=',sqrt(x1));
        writeln('Nghiem x2=',-sqrt(x1));
       end
      else write('PT_vn');
      if x1>0 then
       begin
        writeln('Nghiem x1=',sqrt(x2));
        writeln('Nghiem x2=',-sqrt(x2));
       end
      else write('PT_vn');
            end;      end;
         end;
readln;
end.