The sum of all values of $\theta \, \in \,\left( {0,\frac{\pi }{2}} \right)$ satisfying ${\sin ^2}\,2\theta  + {\cos ^4}\,2\theta  = \frac{3}{4}$ is

  • [JEE MAIN 2019]
  • A

    $\pi $

  • B

    $\frac{{5\pi }}{4}$

  • C

    $\frac{{\pi }}{2}$

  • D

    $\frac{{3\pi }}{8}$

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