JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Critical Thinking

  • question_answer
    If \[\tan \theta =-\frac{1}{\sqrt{3}}\]and \[\sin \theta =\frac{1}{2}\], \[\cos \theta =-\frac{\sqrt{3}}{2}\], then the principal value of \[\theta \] will be [MP PET 1983, 84]

    A) \[\frac{\pi }{6}\]

    B) \[\frac{5\pi }{6}\]

    C) \[\frac{7\pi }{6}\]

    D) \[-\frac{\pi }{6}\]

    Correct Answer: B

    Solution :

    \[\tan \theta =\frac{-1}{\sqrt{3}}=\tan \left( \pi -\frac{\pi }{6} \right)\], \[\sin \theta =\frac{1}{2}=\sin \left( \pi -\frac{\pi }{6} \right)\] and \[\cos \theta =\frac{-\sqrt{3}}{2}\]= \[\cos \left( \pi -\frac{\pi }{6} \right)\] Hence principal value is \[\theta =\frac{5\pi }{6}\].


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