x × (x-7)=0
⇒ \(\left[ \begin{array}{l}x=0\\x-7=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=0\\x=7\end{array} \right.\)
Vậy x∈ {0; 7}
x × (x+11)=0
⇒ \(\left[ \begin{array}{l}x=0\\x+11=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=0\\x=-11\end{array} \right.\)
Vậy x∈ {0; -11}
(x+8) × (x-12)=0
⇒ \(\left[ \begin{array}{l}x+8=0\\x-12=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=-8\\x=12\end{array} \right.\)
Vậy x ∈ {-8; 12}
(x-3 ) × (x ²+3)=0
⇒ \(\left[ \begin{array}{l}x-3=0\\x²+3=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=3\\x²=-3 (vô lí)\end{array} \right.\)
Vậy x = 3
