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phuongthao_94tq


:[TEX]\left{\begin{a^2+b^2+c^2=2}\\{ab+ac+bc=1} [/TEX]
Cm:-4<a+b+c<4
Áp dụng:3(a^2+b^2+c^2)\geq(a+b+c)^2
Cm:-4<a+b+c<4
Áp dụng:3(a^2+b^2+c^2)\geq(a+b+c)^2
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