JEE Main & Advanced Mathematics Trigonometric Identities Question Bank Self Evaluation Test - Trigonometric Function

  • question_answer
    Which one of the following is one of the solutions of the equation of the equation\[\tan 2\theta .\tan \theta =1\]?

    A) \[\pi /12\]          

    B) \[\pi /6\]

    C)  \[\pi /4\]           

    D) \[\pi /3\]

    Correct Answer: B

    Solution :

    \[\tan 2\theta .tan\theta =1\] \[\Rightarrow \,\,\,\frac{2\tan \theta }{1-{{\tan }^{2}}\theta }.\tan \theta =1\] \[\Rightarrow \,\,2{{\tan }^{2}}\theta =1-{{\tan }^{2}}\theta \Rightarrow 3{{\tan }^{2}}\theta =1\] \[\Rightarrow \,\,\,{{\tan }^{2}}\theta =\frac{1}{3}={{\left( \frac{1}{\sqrt{3}} \right)}^{2}}\] \[\Rightarrow \,\,\,{{\tan }^{2}}\theta ={{\tan }^{2}}(30{}^\circ )={{\tan }^{2}}\left( \frac{\pi }{6} \right)\] \[\left[ \because \,\,\,\theta =n\pi \pm \frac{\pi }{6} \right];\]   \[\therefore \,\,\theta =\frac{\pi }{6}\]


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