[tex]2\sqrt{2}cos2x+sin2xcos(x+3pi/4)-4sin(x+pi/4)=0[/tex]
[tex]t=x+\frac{\pi}{4}[/tex]
[tex]2\sqrt{2}cos(2t-\frac{\pi}{2})+sin(2t-\frac{\pi}{2})cos(t+\frac{\pi}{2})-4sint=0[/tex]
[tex] \Leftrightarrow 2\sqrt{2}sin2t+cos2tsint-4sint=0[/tex]
[tex] \Leftrightarrow 4\sqrt{2}sintcost+cos2tsint-4sint=0[/tex]
[tex] \Leftrightarrow sint=0[/tex]
[tex] or 4\sqrt{2}cost+cos2t-4=0 \Leftrightarrow 2cos^2t+4\sqrt{2}cost-5=0[/tex]
dễ r nhỉ
