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

  • question_answer
    If \[\tan \theta +\tan 2\theta +\tan 3\theta =\tan \theta \tan 2\theta \tan 3\theta \], then the general value of \[\theta \]is

    A) \[n\pi \]

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

    C) \[n\pi -\frac{\pi }{4}\pm \alpha \]

    D) \[\frac{n\pi }{2}\]

    Correct Answer: B

    Solution :

    \[\tan \theta +\tan 2\theta +\tan 3\theta =\tan \theta \tan 2\theta \tan 3\theta \] \[\tan 6\theta =\frac{\tan \theta +\tan 2\theta +\tan 3\theta -\tan \theta \tan 2\theta \tan 3\theta }{1-\sum \tan \theta \tan 2\theta }\]            = 0, (from the given condition) \[\Rightarrow \] \[6\theta =n\pi \Rightarrow \theta =n\pi /6\]. Trick:  In such type of problems, the general value of \[\theta \] is given by\[\frac{n\pi }{\text{sum of number of }\theta }\]. So the general value of \[\theta \] is\[\frac{n\pi }{1+2+3}=\frac{n\pi }{6}\].


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