Tìm x biết (x – 2)(x + 4) = 0.

Ta có:

(x – 2)(x + 4) = 0

\( \Leftrightarrow \left[ \begin{array}{l}x - 2 = 0\\x + 4 = 0\end{array} \right.\) \( \Leftrightarrow \left[ \begin{array}{l}x = 2\\x = - 4\end{array} \right.\)

Vậy x = 2 hoặc x = – 4.