CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2003

  • question_answer
    The general solution of the equation \[\tan 2\theta \,.\,\tan \theta =1\] for \[n\in z\] is, \[\theta \] is equal to:

    A)  \[(2n+1)\frac{\pi }{4}\]                

    B)  \[(2n+1)\frac{\pi }{6}\]

    C)  \[(2n+1)\frac{\pi }{2}\]                

    D)  \[\frac{1}{1}(2n+1)\frac{\pi }{3}\]

    Correct Answer: B

    Solution :

    We have                 \[\tan 2\theta \,.\,\,\tan \theta =1\] \[\Rightarrow \]                               \[\tan 2\theta =\frac{1}{\tan \theta }\] \[\Rightarrow \]                               \[\tan 2\theta =\cot \theta \] \[\Rightarrow \]                               \[\tan 2\theta =\tan \left( \frac{\pi }{2}-\theta  \right)\]                                                 \[\left[ \cot \theta =\tan \left( \frac{\pi }{2}-\theta  \right) \right]\] \[\Rightarrow \]               \[2\theta =\frac{\pi }{2}-\theta \] \[\Rightarrow \]               \[3\theta =n\pi +\frac{\pi }{2}\] \[\Rightarrow \]               \[3\theta =(2n+1)\pi /2\] \[\Rightarrow \]               \[\theta =\frac{\pi }{6}\,(2n+1)\]


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