a, | 9 + 2x | =11
⇔\(\left[ \begin{array}{l}9+2x=11\\9+2x=-11\end{array} \right.\)⇔\(\left[ \begin{array}{l}2x=2\\2x=-20\end{array} \right.\)⇔\(\left[ \begin{array}{l}x=1\\x=-10\end{array} \right.\)
Vậy x=1 hoặc x=-10
b, -12 . ( x - 5 ) + 8 = 4x + 20
⇔-12x + 60 + 8 = 4x + 20
⇔-12x - 4x = 20 - 60 - 8
⇔-16x = -48
⇔x = -48 : (-16)
⇔x = 3
Vậy x = 3.