$\tan \frac{A}{2} = . . .$

  • A

    $ \pm \sqrt {\frac{{1 - \sin A}}{{1 + \sin A}}} $

  • B

    $ \pm \sqrt {\frac{{1 + \sin A}}{{1 - \sin A}}} $

  • C

    $ \pm \sqrt {\frac{{1 - \cos A}}{{1 + \cos A}}} $

  • D

    $ \pm \sqrt {\frac{{1 + \cos A}}{{1 - \cos A}}} $

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