$Câu a:$
program a;
uses crt;
var n,i,S: integer;
Begin
clrscr;
write('Nhap n: '); readln(n);
for i:=1 to n do S:=S+i;
write('S = ',S);
readln
End.
$Câu b:$
program b;
uses crt;
var n,i: integer;
S: real;
Begin
clrscr;
write('Nhap n: '); readln(n);
for i:=1 to n do S:=S+1/i;
write('S = ',S:2:2);
readln
End.
$Câu c:$
program a;
uses crt;
var n,i,S: integer;
Begin
clrscr;
write('Nhap n: '); readln(n);
for i:=1 to n do S:=S+2*i;
write('S = ',S);
readln
End.