`a) (x+5).(x-4)=0`
Vì : `(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 ∈ { -5 ; 4 }`
`b)(x-1).(x-3)=0`
Vì : `(x-1).(x-3)=0 `
\(\left[ \begin{array}{l}x-1=0\\x-3=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=0+1\\x=0+3\end{array} \right.\)
\(\left[ \begin{array}{l}x=1\\x=3\end{array} \right.\)
Vậy : ` x ∈ { 1 ; 3 } `
` c)(3-x).(x-3)=0 `
Vì : `(3-x).(x-3)=0`
\(\left[ \begin{array}{l}3-x=0\\x-3=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=3-0\\x=0+3\end{array} \right.\)
\(\left[ \begin{array}{l}x=3\\x=3\end{array} \right.\)
Vậy ` x = 3 `
`d)x.(x+1)=0`
Vì : x.(x+1)=0
\(\left[ \begin{array}{l}x=0\\x+1=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=0\\x=0-1\end{array} \right.\)
\(\left[ \begin{array}{l}x=0\\x=-1\end{array} \right.\)
Vậy ` x ∈ { 0 ; -1 } `
