$$\eqalign{
& \sin 2x.\cot 2x = 0 \cr
& DKXD:\,\,\sin 2x \ne 0 \Leftrightarrow x \ne {{k\pi } \over 2}\,\,\left( {k \in Z} \right) \cr
& PT \Leftrightarrow \sin 2x.{{\cos 2x} \over {\sin 2x}} = 0 \cr
& \Leftrightarrow \cos 2x = 0 \Leftrightarrow 2x = {\pi \over 2} + k\pi \Leftrightarrow x = {\pi \over 4} + {{k\pi } \over 2}\,\,\left( {k \in Z} \right)\,\,\left( {tm} \right) \cr} $$
