Cách giải:
$a,(-x+5)(3-x)=0$
$\to (x-5)(x-3)=0$
$\to \left[ \begin{array}{l}x-5=0\\x-3=0\end{array} \right.$
$\to \left[ \begin{array}{l}x=5\\x=3\end{array} \right.$
Vậy x=5 hoặc x=3
$b,x(x+2)(7-x)=0$
$\to \left[ \begin{array}{l}x=0\\x+2=0\\7-x=0\end{array} \right.$
$\to \left[ \begin{array}{l}x=0\\x=-2\\x=7\end{array} \right.$
Vậy x=0 hoặc x=-2 hoặc x=7
$c,(x-1)(x-2)(-x-3)=0$
$\to (x-1)(x-2)(x+3)=0$
$\to \left[ \begin{array}{l}x-1=0\\x-2=0\\x+3=0\end{array} \right.$
$\to \left[ \begin{array}{l}x=1\\x=2\\x=-3\end{array} \right.$
Vậy x=1 hoặc x=1 hoặc x=-3
