Решите тригонометрическое уравнение: Cos2x+cos6x=cos4x

Решите задачу:

$cos2x+cos6x=cos4x\\ \\ 2cos\frac{2+6}{2}x*cos\frac{2-6}{2}x=cos4x\\ 2cos4xcos2x=cos4x\\ \\ 2cos4xcos2x-cos4x=0\\ cos4x(2cos2x-1)=0\\ \\ cos4x=0\\ 4x=\frac{\pi}{2}+\pi k , k \in Z\\x=\frac{\pi}{8}+\frac{\pi}{4}k , k \in Z \\ \\ 2cos2x=1\\ cos2x=\frac{1}{2}\\ 2x=\pm \frac{\pi}{3}+2\pi k , k \in Z\\ x= \pm \frac{\pi}{12}+\pi k , k \in Z$