Bài 5 :
a) $(x+5)(x-4)=0$
$⇔\left[ \begin{array}{l}x+5=0\\x-4=0\end{array} \right. $
$⇔\left[ \begin{array}{l}x=-5\\x=4\end{array} \right. $
b) $(x-1)(x-3)=0$
$⇔\left[ \begin{array}{l}x-1=0\\x-3=0\end{array} \right. $
$⇔\left[ \begin{array}{l}x=1\\x=3\end{array} \right. $
c) $(3-x)(x-3)=0$
$⇔ (x-3)^2 =0 $
$⇔x-3=0$
$⇔x=3$
D) $x(x+1)=0$
$⇔\left[ \begin{array}{l}x=0\\x+1=0\end{array} \right. $
$⇔\left[ \begin{array}{l}x=0\\x=-1\end{array} \right. $
e) $4-(27-3)=x-(13-4)$
$⇔-20=x-9$
$⇔x=-11$
f) $8-(x-10)=23-(-4+12)$
$⇔8-x+10=23+4-12$
$⇔x=18-23+12-4$
$⇔x=3$
Chúc bạn học tốt !