Đáp án:
$$\,D = R\backslash \left\{ {k\pi ;\,\,k \in Z} \right\}$$
Giải thích các bước giải:
$$\eqalign{
& y = {{\cot x} \over {\cos x - 1}} \cr
& Ham\,\,so\,\,xac\,\,dinh \cr
& \Leftrightarrow \left\{ \matrix{
\sin x \ne 0 \hfill \cr
\cos x \ne 1 \hfill \cr} \right. \Leftrightarrow \left\{ \matrix{
x \ne k\pi \hfill \cr
x \ne k2\pi \hfill \cr} \right. \Leftrightarrow x \ne k\pi \,\,\left( {k \in Z} \right) \cr
& \Rightarrow TXD:\,\,D = R\backslash \left\{ {k\pi ;\,\,k \in Z} \right\} \cr} $$
