Đáp án:
\(\left\{ \begin{array}{l}
x \ne \dfrac{\pi }{8} + \dfrac{{k\pi }}{4}\\
x \ne \dfrac{\pi }{4} + k2\pi \\
x \ne \dfrac{{3\pi }}{4} + k2\pi
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
DK:\left\{ \begin{array}{l}
\cos 4x \ne 0\\
2\sin x - \sqrt 2 \ne 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
\cos 4x \ne 0\\
\sin x \ne \dfrac{{\sqrt 2 }}{2}
\end{array} \right.\\
\to \left\{ \begin{array}{l}
4x \ne \dfrac{\pi }{2} + k\pi \\
x \ne \dfrac{\pi }{4} + k2\pi \\
x \ne \dfrac{{3\pi }}{4} + k2\pi
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x \ne \dfrac{\pi }{8} + \dfrac{{k\pi }}{4}\\
x \ne \dfrac{\pi }{4} + k2\pi \\
x \ne \dfrac{{3\pi }}{4} + k2\pi
\end{array} \right.
\end{array}\)
