[กิตติ]

$A^2+B^2+C^2-AB-BC-CA=0 $

$2(\frac{A}{2} -\frac{B}{2} )^2+2(\frac{B}{2} -\frac{C}{2})^2+2(\frac{A}{2} -\frac{C}{2})^2=0$

$A=B=C$

$A=log_xy ,B=log_xz ,C=1$

$log_xy=1\rightarrow x=y$

$log_xz=1\rightarrow x=z$

$x=y=z$