If $0 \le x \le \pi $ and ${81^{{{\sin }^2}x}} + {81^{{{\cos }^2}x}} = 30$, then $x =$

  • [JEE MAIN 2021]
  • A

    $\pi /6$

  • B

    $\pi /2$

  • C

    $\pi /4$

  • D

    $3\pi /4$

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