Oái, tự nhien quên mất chủ đề này. Thành thật xin lỗi các bạn!
Đây là lời giải!
Nếu
http://dientuvietnam...?a_{n 1}(1-3a_n)=1-3a_{n+1}
http://dientuvietnam.net/cgi-bin/mimetex.cgi?a_n(1-3a_{n-1})=1-3a_n
............................................
http://dientuvietnam.net/cgi-bin/mimetex.cgi?a_2(1-3a_1)=1-3a_2
http://dientuvietnam.net/cgi-bin/mimetex.cgi?3a_{n+1}(1-a_n)=1-a_{n+1}
http://dientuvietnam.net/cgi-bin/mimetex.cgi?3a_n(1-a_{n-1})=1-a_n
..........................................
http://dientuvietnam.net/cgi-bin/mimetex.cgi?3a_2(1-a_1)=1-a_2
http://dientuvietnam.net/cgi-bin/mimetex.cgi?a=1 hoặc
thì dễ rồi!
OK!