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a) |x + 3| = 11
⇒\(\left[ \begin{array}{l}x+3=11\\x+3=-11\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=11-3=8∈Z\\x=-11-3=-14∈Z\end{array} \right.\)
Vậy x∈{8; -14}
b) |x - 4| = 5 + 8
⇒|x - 4| =13
⇒\(\left[ \begin{array}{l}x-4=13\\x-4=-13\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=13+4=17∈Z\\x=-13+4=-9∈Z\end{array} \right.\)
Vậy x∈{17; -9}