Đáp án:
$a) (x-3)(6+2x)=0$
$⇔$\(\left[ \begin{array}{l}x-3=0\\6+2x=0\end{array} \right.\)
$⇔$\(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
$\text{Vậy S={3 ; -3}}$
$b) x^2 -4x =0$
$⇔x(x-4)=0$
$⇔$\(\left[ \begin{array}{l}x=0\\x-4=0\end{array} \right.\)
$⇔$\(\left[ \begin{array}{l}x=0\\x=4\end{array} \right.\)
$\text{Vậy S={0 ; 4} }$
$c) (x-2)^2 -2x+4 =0$
$⇔(x-2)^2 -2(x-2)=0$
$⇔(x-2)(x-2 -2)=0$
$⇔(x-2)(x-4)=0$
$⇔$\(\left[ \begin{array}{l}x-2=0\\x-4=0\end{array} \right.\)
$⇔$\(\left[ \begin{array}{l}x=2\\x=4\end{array} \right.\)
$\text{Vậy S={2 ; 4}}$
