The general value $\theta $ is obtained from the equation $\cos 2\theta = \sin \alpha ,$ is

  • A

    $2\theta = \frac{\pi }{2} - \alpha $

  • B

    $\theta = 2n\pi \pm \left( {\frac{\pi }{2} - \alpha } \right)$

  • C

    $\theta = \frac{{n\pi + {{( - 1)}^n}\alpha }}{2}$

  • D

    $\theta = n\pi \pm \left( {\frac{\pi }{4} - \frac{\alpha }{2}} \right)$

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