Сos п/7* sin2x + sin п/7* cos2x=-1/2 помогите !!!

$cos \frac{ \pi }{7} * sin2x + sin \frac{ \pi }{7}* cos2x=-\frac{1}{2}$

$sin(2x + \frac{ \pi }{7})=- \frac{1}{2}$

$2x + \frac{ \pi }{7}=- \frac{ \pi }{2} +2 \pi n,$    $n$ ∈ $Z$

$2x =- \frac{ \pi }{2}- \frac{ \pi }{7} +2 \pi n,$    $n$ ∈ $Z$

$2x =- \frac{9 \pi }{14} +2 \pi n,$    $n$ ∈ $Z$

$x =- \frac{9 \pi }{28} + \pi n,$    $n$ ∈ $Z$