. UCLN(u, u) > 1 v´o,i m.oi u∈ U. H˜ay¯dê, thi ´t l.âpS = 1, 2, , 98. X´ac¯d.inh gi´a tr.i tô´i thi ,u l`a sô´nguyên du,o,ng n r`˘ang,¯dô´i. TO´AN C´AC NU,´O,C1998 – 199957 Ð`Ê THI V`A L`O,I GI,AI(T.âp 1)NH`A XU´ÂT B,AN GI´AO D.UC20 Chu,o,ng 3. Ðê` thi olympic to´an Trung Quô´cKhir = 4Rsinα2sinβ2sinγ2,Ch´ung. c´o thê,¯du,.o,c gi,ai quyê´t m.ôt c´ach d˜ê d`ang .14 Chu,o,ng 2. Ðê` thi Olympic To´an CanadaL`o,i gi,ai 2.3. Ch´ung tôi ch´u,ng minh r`˘angn(1 +13+...