The principal solutions of $\cos 2x = -\frac{1}{2}$ are

  • A
    $x = \frac{\pi}{3}, x = \frac{2\pi}{3}$
  • B
    $x = \frac{\pi}{3}, x = \frac{5\pi}{6}$
  • C
    $x = \frac{2\pi}{3}, x = \frac{4\pi}{3}$
  • D
    $x = \frac{\pi}{6}, x = \frac{5\pi}{6}$

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