cos(4х+П/4)=- корень из 2/2 объясните как решать!!

$cos (4x+\frac{\pi}{4})=-\frac{\sqrt{2}}{2};\\ 4x+\frac{\pi}{4}= ^+_-arccos (-\frac{\sqrt{2}}{2})+2*\pi*k;\\ 4x+\frac{\pi}{4}= ^+_-(\pi-arccos (\frac{\sqrt{2}}{2}))+2*\pi*k;\\ 4x+\frac{\pi}{4}= ^+_-(\pi-\frac{\pi}{4})+2*\pi*k;\\ 4x+\frac{\pi}{4}= ^+_-(\frac{3\pi}{4})+2*\pi*k;\\ 4x=-\frac{\pi}{4} ^+_-(\frac{3\pi}{4})+2*\pi*k;\\ x=-\frac{\pi}{16} ^+_-\frac{3\pi}{16}+\frac{\pi}{2}*k$

k є Z