$x² -2x + y² + 4y + 4z² - 4z + 6 = 0$
$x² -2x + y² + 4y + 4z² - 4z + 1 + 1 +4= 0 $
$(x² -2x + 1)+( y² + 4y+4)+(4z² - 4z +1) = 0 $
$(x-1)² + (y+2)² + (2z-1)² = 0 $
Mà
$(x-1)² ≥ 0 $
$(y+2)²≥ 0$
$(2x+1)² ≥ 0$
⇔
$(x-1)² = 0 $
$x-1 = 0$
$x =1$
_________
$(y+2)²= 0$
$y+2 = 0$
$y= -2$
________
$(2z-1)²=0$
$2z-1=0$
$2z = 1$
$z = \dfrac{1}{2}$
___________Hết ____________
