Ap dung Co si ta co 2 3 3 3 3 a a b a a b b c bc abc + + ≥ = Tuong tu ta co 2 3 3 3 3 b b c b b c c a ca abc + + ≥ = 2 3 3 3 3 c c a c c a a b ab abc + + ≥ = Cong ve ta co 3 a b c a b c b c a abc + + + + ≥ Do abc 1 ≤ ⇒ ( ) a b c a b c dpcm b c a + + ≥ + +