Đáp án:
$\left[\begin{array}{l}x = \dfrac{\pi}{8}+k\dfrac{\pi}{4}\\x = k\dfrac{\pi}{3}\end{array}\right.\quad (k\in\Bbb Z)$
Giải thích các bước giải:
$(\cos^22x - \sin^22x).\sin3x = 0$
$\Leftrightarrow \cos4x.\sin3x = 0$
$\Leftrightarrow \left[\begin{array}{l}\cos4x = 0\\\sin3x = 0\end{array}\right.$
$\Leftrightarrow \left[\begin{array}{l}x = \dfrac{\pi}{8}+k\dfrac{\pi}{4}\\x = k\dfrac{\pi}{3}\end{array}\right.\quad (k\in\Bbb Z)$
