$4(sin^4x+cos^4x)+sin4x-2=0$<=>$4(sin^2x+cos^2x)^2-8sin^2x.cos^2x+sin4x-2=0$<=>$1-2sin^22x+sin4x+1=0$<=>$cos4x+sin4x=-1$<=>$cos(\frac{\pi}{4}-4x)=-\frac{\sqrt{2}}{2}$Dạng cơ bản rồi!
$4(sin^4x+cos^4x)+sin4x-2=0$<=>$4(sin^2x+cos^2x)^2-8sin^2x.cos^2x+sin4x-2=0$<=>$1-2sin^2x+sin4x+1=0$<=>$cos4x+sin4x=-1$<=>$cos(\frac{\pi}{4}-4x)=-\frac{\sqrt{2}}{2}$Dạng cơ bản rồi!
$4(sin^4x+cos^4x)+sin4x-2=0$<=>$4(sin^2x+cos^2x)^2-8sin^2x.cos^2x+sin4x-2=0$<=>$1-2sin^2
2x+sin4x+1=0$<=>$cos4x+sin4x=-1$<=>$cos(\frac{\pi}{4}-4x)=-\frac{\sqrt{2}}{2}$Dạng cơ bản rồi!