$$\sin 2 x + \cos ( \frac { 3 \pi } { 2 } + 6 x ) = \sin 4 x$$
$x=\pi n_{2}+\frac{\pi }{6}\text{, }n_{2}\in \mathrm{Z}$
$x=\pi n_{3}+\frac{5\pi }{6}\text{, }n_{3}\in \mathrm{Z}$
$x=\frac{\pi n_{1}}{4}\text{, }n_{1}\in \mathrm{Z}$
