JEE Main & Advanced Sample Paper JEE Main - Mock Test - 12

  • question_answer
    General values of \[\theta \] satisfying the equation \[{{\tan }^{2}}\theta +\sec 2\theta =1\] is

    A) \[n\pi \]                        

    B) \[n\pi +\frac{\pi }{3}\]

    C) \[n\pi -\frac{\pi }{3}\]            

    D) All of these

    Correct Answer: D

    Solution :

    Using \[\sec 2\theta =\frac{1}{\cos 2\theta }=\frac{1+{{\tan }^{2}}\theta }{1-{{\tan }^{2}}\theta }\]
    Given equation is: \[{{\tan }^{2}}\theta +\frac{1+{{\tan }^{2}}\theta }{1-{{\tan }^{2}}\theta }=1\]
    \[\Rightarrow \,\,\,{{\tan }^{2}}\theta (3-{{\tan }^{2}}\theta )=0\]
    \[\Rightarrow \,\,\,\tan \theta =0\] or \[\pm \sqrt{3}\]
    Thus \[\theta =m\pi ,\] \[n\pi \pm \pi /3\] where m and n are integers.


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