Cho B = {x ∈ R : /x-1/ < 3} C = {m, m + 4} Tìm m để B ⊂ C

$$\eqalign{ & B = \left\{ {x \in R:\,\,\left| {x - 1} \right| < 3} \right\} \cr & C = \left[ {m;m + 4} \right] \cr & \left| {x - 1} \right| < 3 \cr & \Leftrightarrow - 3 < x - 1 < 3 \cr & \Leftrightarrow - 2 < x < 4 \cr & \Rightarrow B = \left( { - 2;4} \right) \cr & B \subset C \Leftrightarrow m \le - 2 < 4 \le m + 4 \cr & \Leftrightarrow \left\{ \matrix{ m \le - 2 \hfill \cr m \ge 0 \hfill \cr} \right. \Leftrightarrow m \in \emptyset \cr} $$