a) |2x + 1| - 19 = -7
⇒ |2x +1| = -7 +19
⇒ |2x +1| = 12
⇒ \(\left[ \begin{array}{l}2x+1=12\\2x+1=-12\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=\frac{11}{2}\\x=\frac{-13}{2}\end{array} \right.\)
Vậy x ∈ { $\frac{11}{2}$ ; $\frac{-13}{2}$ }
b) -28 – 7. |- 3x + 15| = -70
⇒ |-3x +15| = $\frac{-28 +70}{7}$
⇒ |-3x +15| = 6
⇒ \(\left[ \begin{array}{l}-3x+15=6\\-3x+15=-6\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=3\\x=7\end{array} \right.\)
Vậy x ∈ {3; 7}
c) 18 – 2. |-x + 5| = 12
⇒ |-x +5| = $\frac{18 -12}{2}$
⇒ |-x +5| = 3
⇒ \(\left[ \begin{array}{l}-x+5=3\\-x+5=-3\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=2\\x=8\end{array} \right.\)
Vậy x ∈ {2; 8}
