$$\eqalign{
& f\left( x \right) = \left\{ \matrix{
{1 \over {x - 3}}\,\,khi\,\,x < 2 \hfill \cr
\sqrt {4 - \left| x \right|} \,\,khi\,\,x > 2 \hfill \cr} \right. \cr
& DKXD:\,\,\left\{ \matrix{
x \ne 3\,\,\left( {luon\,\,dung\,\,\forall \,\,x < 2} \right) \hfill \cr
4 - \left| x \right| \ge 0 \hfill \cr} \right. \Leftrightarrow \left| x \right| \le 4 \Leftrightarrow - 4 \le x \le 4 \cr
& Ket\,\,hop\,\,DK \Rightarrow 2 < x \le 4 \cr
& \Rightarrow TXD:\,\,D = \left( { - \infty ;2} \right) \cup \left( {2;4} \right] \cr} $$
