`a,x(x+7)=0`
`⇔` \(\left[ \begin{array}{l}x=0\\x+7=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=0\\x=-7\end{array} \right.\)
`b,(x+12)(x-3)=0`
`⇔` \(\left[ \begin{array}{l}x+12=0\\x-3=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=-12\\x=3\end{array} \right.\)
`c,(-x+5)(3-x)=0`
`⇔` \(\left[ \begin{array}{l}-x+5=0\\3-x=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=5\\x=3\end{array} \right.\)
`d,(x-1)(x+2)(-3)=0`
`⇔(x-1)(x+2)=0`
⇔` \(\left[ \begin{array}{l}x-1=0\\x+2=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=1\\x=-2\end{array} \right.\)
