2x2 + y2 + 9 = 2xy + 6x
x2 - 2xy + y2 + x2 - 6x + 9 = 0
(x - y)2 + (x - 3)2 = 0
\(\left[\begin{matrix}x-y=0\\x-3=0\end{matrix}\right.\)
\(\left[\begin{matrix}x=y\\x=3\end{matrix}\right.\)
x = y = 3
x2-2xy+y2+x2-6x+9=0
(x-y)2+(x-3)2=0
suy ra x-y=0 hoặc x-3=0
x=y hoặc x=3
suy ra x=y=3