Solve: \(2\cos x - 1 = 0\).

  • A \((\frac{2\pi}{3}, \frac{4\pi}{3})\)
  • B \((\frac{\pi}{6}, \frac{5\pi}{6})\)
  • C \((\frac{\pi}{5}, \frac{2\pi}{5})\)
  • D \((\frac{\pi}{3}, \frac{5\pi}{3})\)
waec 2015furthermathematics

The correct answer is D. \((\frac{\pi}{3}, \frac{5\pi}{3})\)

\(2\cos x - 1 = 0 \implies 2\cos x = 1\)

\(\cos x = \frac{1}{2}\)

\(x = \cos^{-1} (\frac{1}{2})\)

= \(\frac{\pi}{3}\) = \(\frac{5\pi}{3}\)

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