a. $|x-3|-7=13 $
⇔ $|x-3|=13+7 $
⇔ $|x-3|=20 $
⇔ \(\left[ \begin{array}{l}x-3=20\\x-3=-20\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=20+3\\x=-20+3\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=23\\x=-17\end{array} \right.\)
Vậy $x=23$ hoặc $x=-17$
b. $72-3.|x+1|=9 $
⇔ $3.|x+1|=72-9$
⇔ $3.|x+1|=63$
⇔ $|x+1|=21$
⇔ \(\left[ \begin{array}{l}x+1=21\\x+1=-21\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=21-1\\x=-21-1\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=20\\x=-22\end{array} \right.\)
Vây $x=20$ hoặc $x=-22$
c. $17-(43-|x|)=45$
⇒ $43-|x|=17-45$
⇒ $43-|x|=-28$
⇒ $|x|=43-(-28)$
⇒ $|x|=43+28$
⇒ $|x|=71$
⇒ \(\left[ \begin{array}{l}x=71\\x=-71\end{array} \right.\)
Vậy $x=71$ hoặc $x=-71$
