a/ (x+5) . (x – 4) = 0 b/ (x – 1) . (x - 3) = 0

`a) (x+5) . (x-4) = 0`

`=>` \(\left[ \begin{array}{l}x+5 = 0\\x-4 = 0\end{array} \right.\) 

`=>` \(\left[ \begin{array}{l}x = 0-5\\x=0+4\end{array} \right.\) 

`=>` \(\left[ \begin{array}{l}x = -5\\x=4\end{array} \right.\) 

Vậy `x \in {-5;4}`

`b) (x-1) . (x-3) = 0`

`=>` \(\left[ \begin{array}{l}x-1 = 0\\x-3 = 0\end{array} \right.\) 

`=>` \(\left[ \begin{array}{l}x=0+1\\x=0+4\end{array} \right.\) 

`=>` \(\left[ \begin{array}{l}x=1\\x=4\end{array} \right.\) 

Vậy `x \in {1;4}`