xl m.n

6

654321sss

[TEX][/TEX]ta có:đề ra \Leftrightarrow
a^2/3+b^2+c^2-ab+bc+ca>0
\Leftrightarrowa^2/4+b^2+c^2-ac-ab+2bc+
a^2/12-3bc>0
\Leftrightarrow(a/2-b-c)^2+(a^3-36abc)/12a>0 (*)
(*) luôn đúng vì (a/2-b-c)^2\geq0 và
(a^3-36abc)/12a=(a^3-36)/12a>0
suy ra đpcm
:khi (197):
:M056:
 
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