The real roots of the equation $cos^7x\,  +\,  sin^4x\,  =\,  1$  in the interval $(-\pi, \pi)$ are

  • A

    $ \{- \frac{\pi }{2}\,,\,0 \}$

  • B

    $\{ - \frac{\pi }{2}\,,\,0\,,\,\frac{\pi }{2} \}$

  • C

    $\{ \frac{\pi }{2}\,,\,0 \}$

  • D

    $\{ 0\,\,,\,\,\frac{\pi }{4}\,\,,\,\frac{\pi }{2} \}$

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