AB=sqrt((x_(B)-x_(A))^2+(y_(B)-y(A))^2+(z_(B)-z_(A))^2)
AC=sqrt((1-1)^2+(2-0)^2+(2-0)^2)=sqrt(4+4)=sqrt(8)
AB=sqrt((x-1)^2+(0-0)^2+(2-0)^2)=sqrt((x-1)^2+4)
АВ=АС
sqrt((x-1)^2+4)=sqrt(8)
Возводим в квадрат
(x-1)^2+4=8
(х-1)^2=8-4
(х-1)^2=4
x-1=2 или x-1=-2
x=3 или x=-1