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