`(x-5).(x-7)=0`
`<=>`\(\left[ \begin{array}{l}x-5=0\\x-7=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0+5\\x=0+7\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=5\\x=7\end{array} \right.\)
`=> x in {5;7}`
`(x-3).(3+x)=0`
`<=>`\(\left[ \begin{array}{l}x-3=0\\3+x=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0+3\\x=0-3\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
`=> x in {3;-3}`
