Từ GT
\Rightarrow ${(x-y)^2}-{(x+y-2z)^2}+{(y-z)^2}-{(y+z-2x)^2}+{(z-x)^2}-{(z+x-2y)^2}=0$
\Leftrightarrow $(x-y-x-y+2z)(x-y+x+y-2z)+(y-z-y-z+2x)(y-z+y+z-2x)+(z-x-z-x+2y)(z-x+z+x-2y)=0$
\Leftrightarrow $4(z-y)(x-z)+4(x-z)(y-x)+4(y-x)(z-y)=0$
\Leftrightarrow $(z-y)(x-z)+(x-z)(y-x)+(y-x)(z-y)=0$
\Leftrightarrow ${x^2}+{y^2}+{z^2}-xy-yz-zx=0$
\Leftrightarrow ${(x-y)^2}+{(y-z)^2}+{(z-x)^2}=0$
\Rightarrow x=y=z