Đáp án:
\(\left[ \begin{array}{l}
x = \dfrac{\pi }{8} + \dfrac{{k\pi }}{4}\\
x = k\pi
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
DK:\cos x \ne 0\\
\to x \ne \dfrac{\pi }{2} + k\pi \\
{\cos ^3}4x.\dfrac{{\sin x}}{{\cos x}} = 0\\
\to \left[ \begin{array}{l}
\cos 4x = 0\\
\sin x = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
4x = \dfrac{\pi }{2} + k\pi \\
x = k\pi
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = \dfrac{\pi }{8} + \dfrac{{k\pi }}{4}\\
x = k\pi
\end{array} \right.
\end{array}\)
