... Kvant, 1993 61 Cho a, b, c s th c dương Ch ng minh r ng ∑ (1 + a ) (1 + b ) (a − c) (b − c) ≥ (1 + a )(1 + b )(1 + c )(a − b) (b − c) (c − a) 2 2 2 2 2 2 AMM 62 [ Titu Vàreescu, Mircea Lascu ... + z z + zx + x (x + y + z) Gazeta Matematică 97 [ Vasile Cirtoaje ] Cho a, b, c, d s th c dương Ch ng minh r ng (a3 +1)(b3 +1)(c + 1)(d +1) ≥ (1 + abcd )(1 + a )(1 + b )(1 + c )(1 + d ) Gazeta ... ( y + z)+ ( z + x) + ( x + y) ≥ b+c c+a a +b 102 Cho a, b, c s th c dương Ch ng minh r ng 2 (b + c − a ) (c + a − b) (a + b − c) + + ≥ 2 (b + c) + a (c + a) + b (a + b) + c Japan, 1997 12 500...