Đáp án đúng: C
Giải chi tiết:\(\eqalign{ & a)\,\,\,x - 1 = - 9 \cr & \,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\, = - 9 + 1 \cr & \,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\, = - (9 - 1) \cr & \,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\, = - 8. \cr} \)
Vậy \(x=-8.\)
\(\begin{array}{l}b)\,\,\,\left| {x - 2} \right| + 7 = 12\\\,\,\,\,\,\,\,\,\left| {x - 2} \right|\,\,\,\,\,\,\,\,\,\, = 12 - 7\\\,\,\,\,\,\,\,\,\left| {x - 2} \right|\,\,\,\,\,\,\,\,\,\, = 5.\end{array}\)
\(\begin{array}{l}TH1:x - 2 = 5\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\, = 5 + 2\\\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\, = 7.\end{array}\)
\(\begin{array}{l}TH2:\,\,x - 2 = - 5\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\, = - 5 + 2\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\, = - (5 - 2)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\, = - 3.\end{array}\)
Vậy \(x=7\) hoặc \(x=-3.\)