677 x 874 + 251 677 x 874 + 251 677 x 874 + 251 677 x 874 + 251
-------------------------= ----------------------------------- = ------------------------------- = ------------------------------------- = 1
678 x 874 - 623 (677+1) x 874 - 623 677 x 874+874-623 677 x 874 + 251
toi khong biet . tra loigiup roi cau nay voi 677grfbvhnjuiytgrfd