જો $\sin \beta$ એ $\sin \alpha$ અને $\cos \alpha$ વચ્ચેનો સમગુણોત્તર મધ્યક હોય,તો $\cos 2\beta$ બરાબર શું થાય?

  • A
    $2\sin^2\left(\frac{\pi}{4} - \alpha\right)$
  • B
    $2\cos^2\left(\frac{\pi}{4} + \alpha\right)$
  • C
    $2\sin^2\left(\frac{\pi}{4} + \alpha\right)$
  • D
    $(a)$ અને $(b)$ બંને

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