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Không mất tính tổng quát, giả sử: x=max
*) Nếu x\ge y\ge z \Rightarrow x^{19}+y^5\ge y^{19}+z^5
\Rightarrow 1890z+z^{2011}\ge1890x+x^{2011}
\Rightarrow z\ge x\Rightarrow x=y=z
*) Nếu x\ge z\ge y \Rightarrow z^{19}+x^5\ge y^{19}+z^5
\Rightarrow 1890y+y^{2011}\ge1890x+x^{2011}
\Rightarrow y\ge x\Rightarrow x=y=z
Vậy: x=y=z.
Ta có: x^{2011}+1890x=x^{19}+x^5
\Leftrightarrow x(x^{2010}-x^{18}-x^4+1890)=0
\Leftrightarrow x=0
Vậy: x=y=z=0.
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