If $\cos \theta = \frac{1}{2}\left( {x + \frac{1}{x}} \right)$, then $\frac{1}{2}\left( {{x^2} + \frac{1}{{{x^2}}}} \right) = $

  • A

    $\sin 2\theta $

  • B

    $\cos \,2\theta $

  • C

    $\tan \,2\theta $

  • D

    $\sec \,2\theta $

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