a) $(2x+4)(x-2)=0^{}$
$⇔\left[ \begin{array}{l}2x+4=0\\x-2=0\end{array} \right.$
$⇔\left[ \begin{array}{l}x=-2\\x=2\end{array} \right.$
b) $(x-1)^2.(x+5)=0^{}$
$⇔\left[ \begin{array}{l}(x-1)^2=0\\x+5=0\end{array} \right.$
$⇔\left[ \begin{array}{l}x=1\\x=-5\end{array} \right.$
c) $x^2-3x=0^{}$
$⇔x(x-3)=0$
$⇔\left[ \begin{array}{l}x=0\\x=3\end{array} \right.$.
