program oken; uses crt; var i,n:integer; s:real; begin clrscr; write('nhap 1 so bat ky: '); readln(n); s:=0; for i:=2 to n do s:=s + 1/(i*i-1); writeln('tong S la: ',s:0:3); readln; end.
Dùng While-do:
program oken; uses crt; var i,n:integer; s:real; begin clrscr; write('nhap 1 so bat ky: '); readln(n); s:=0; i:=2; while i<=n do begin s:=s + 1/(i*i-1); i:=i+1; end; writeln('tong S la: ',s:0:3); readln; end.
