Bạn tham khảo:
a, $| 2x + 9 | = 15$
$⇔$ \(\left[ \begin{array}{l}2x+9=15\\2x+9=-15\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=3\\x=-12\end{array} \right.\)
b, $25 - | 3 - x | = 10$
$⇔ | 3 - x | = 15$
$⇔$ \(\left[ \begin{array}{l}3-x=15\\3-x=-15\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=-12\\x=18\end{array} \right.\)