If cos⁡θ=12x+1x then 12×2+1×2 is equal to

If cosθ=12x+1x then 12x2+1x2 is equal to

  1. A

    sin 2θ

  2. B

    cos 2θ

  3. C

    tan 2θ

  4. D

    None of these

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    Solution:

    Given that, cosθ=12x+1x

    x+1x=2cosθ----i

    We know that,

    x2+1x2=x+1x22=(2cosθ)22=4cos2θ2=2cos2θ12x2+1x2=12×2cos2θ=cos2θ

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