Toán 7

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tranhainam1801

Vì [TEX]x+y+z=0\Rightarrow x+y=-z[/TEX]
[TEX]y+z=-x[/TEX]
[TEX]z+x=-y[/TEX]
[TEX]\Rightarrow(x+y)(y+z)(z+x)=-xyz=-10[/TEX]
 
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