Cho hàm số \(f(x) = \frac{{\sin 3x}}{3} - \cos x - \sqrt 3 \left( {\sin x - \frac{{\cos 3x}}{3}} \right)\)Giải phương trình \(f(x)

Cho hàm số \(f(x) = \frac{{\sin 3x}}{3} - \cos x - \sqrt 3 \left( {\sin x - \frac{{\cos 3x}}{3}} \right)\)

Giải phương trình \(f'(x) = 0\)

• A. \(\left[ \begin{array}{l}
  x = \frac{\pi }{{12}} + k\pi \\
  x =  - \frac{{3\pi }}{8} + k\frac{\pi }{2}
  \end{array} \right.\left( {k \in Z} \right)\)
• B. \(\begin{array}{l}
  f'(x) = 0\\
  \left[ \begin{array}{l}
  x =  - \frac{\pi }{{12}} + k\pi \\
  x =  - \frac{{3\pi }}{8} + k\frac{\pi }{2}
  \end{array} \right.\left( {k \in Z} \right)
  \end{array}\)
• C. \(\begin{array}{l}
  f'(x) = 0\\
  \left[ \begin{array}{l}
  x =  - \frac{\pi }{{12}} + k\pi \\
  x = \frac{{3\pi }}{8} + k\frac{\pi }{2}
  \end{array} \right.\left( {k \in Z} \right)
  \end{array}\)
• D. \(\begin{array}{l}
  f'(x) = 0\\
  \left[ \begin{array}{l}
  x = \frac{\pi }{{12}} + k\pi \\
  x = \frac{{3\pi }}{8} + k\frac{\pi }{2}
  \end{array} \right.\left( {k \in Z} \right)
  \end{array}\)