Toán 12 Gtnn

C

conga222222

$\eqalign{
& \cos i: \cr
& {a^3} + 9a + {b^3} + 9b + {c^3} + 9c \ge 6\left( {{a^2} + {b^2} + {c^2}} \right) = 162 \cr
& \to {a^3} + {b^3} + {c^3} \ge 162 - 9\left( {a + b + c} \right) \cr
& ma\;cosi: \cr
& 54 = {a^2} + 9 + {b^2} + 9 + {c^2} + 9 \ge 6\left( {a + b + c} \right) \leftrightarrow a + b + c \le 9 \cr
& \to {a^3} + {b^3} + {c^3} \ge 162 - 9*9 = 81 \cr
& dau = \leftrightarrow a = b = c = 3 \cr} $
 
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