JEE Main & Advanced Mathematics Trigonometric Equations Question Bank Solution of trigonometrical equations

  • question_answer
    If \[\tan \theta +\tan 2\theta +\sqrt{3}\tan \theta \tan 2\theta =\sqrt{3},\]then [UPSEAT 2001]

    A) \[\theta =(6n+1)\pi /18,\,\forall n\in I\]

    B) \[\theta =(6n+1)\pi /9,\,\forall n\in I\]

    C) \[\theta =(3n+1)\pi /9,\,\forall n\in I\]

    D) None of these

    Correct Answer: B

    Solution :

     Given relation is \[\tan \theta +\tan 2\theta +\sqrt{3}\tan \theta \tan 2\theta =\sqrt{3}\] Þ  \[\,\tan \theta +\tan 2\theta =\sqrt{3}(1-\tan \theta \tan 2\theta )\] Þ  \[\frac{\tan \theta +\tan 2\theta }{1-\tan \theta \tan 2\theta }\]= \[\sqrt{3}\] Þ  \[\tan 3\theta =\tan (\pi /3)\] Þ  \[3\theta =n\pi +\frac{\pi }{3}\]  Þ \[\theta =(3n+1)\frac{\pi }{9}\].


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