ĐK :
$\cos(x-\frac{\pi}{4})\cos(x+\frac{\pi}{4})\neq 0\Leftrightarrow
x\neq\frac{\pi}{4}+\frac{k\pi}{2}$
$(x+\frac{\pi}{4})=\frac{\pi}{2}+(x-\frac{\pi}{4})\Rightarrow\tan(x+\frac{\pi}{4})=-\cot(x-\frac{\pi}{4})$
$PT\Leftrightarrow\sin^6x+\cos^6x=\frac{1}{4}\Leftrightarrow
1-\frac{3}{4}\sin^22x=\frac{1}{4}$
$\Leftrightarrow\sin^22x=1\Leftrightarrow\cos
2x=0\Leftrightarrow x=\frac{\pi}{4}+\frac{k\pi}{2}, k\in Z$( không thỏa mãn)
Vậy pt vô
nghiệm