$$\eqalign{
& \left( {m + 1} \right)\sin 2x + 2 - m = 0 \cr
& x = {\pi \over {12}}\,\,la\,\,nghiem\,\,cua\,\,pt \cr
& \Rightarrow \left( {m + 1} \right)\sin 2.{\pi \over {12}} + 2 - m = 0 \cr
& \Leftrightarrow \left( {m + 1} \right)\sin {\pi \over 6} + 2 - m = 0 \cr
& \Leftrightarrow {1 \over 2}\left( {m + 1} \right) + 2 - m = 0 \cr
& \Leftrightarrow {1 \over 2}m + {1 \over 2} + 2 - m = 0 \cr
& \Leftrightarrow - {1 \over 2}m + {5 \over 2} = 0 \cr
& \Leftrightarrow {1 \over 2}m = {5 \over 2} \Leftrightarrow m = 5 \cr} $$
