a. $|2x+9|=15$
⇒ \(\left[ \begin{array}{l}2x+9=15\\2x+9=-15\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}2x=15-9\\2x=-15-9\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}2x=6\\2x=-24\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=3\\x=-12\end{array} \right.\)
Vậy $x=-12$ hoặc $x=3$
b. $25-|3-x|=10$
⇒ $|3-x|=25-10$
⇒ $|3-x|=15$
⇒ \(\left[ \begin{array}{l}3-x=15\\3-x=-15\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=3-15\\x=3-(-15)\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=-12\\x=18\end{array} \right.\)
Vậy $x=-12$ hoặc $x=18$
