JCECE Engineering JCECE Engineering Solved Paper-2014

  • question_answer
    The general value of \[\theta \] in the equation\[2\sqrt{3}\cos \theta =\tan \theta \]

    A) \[2n\pi \pm \frac{\pi }{6}\]                         

    B) \[2n\pi \pm \frac{\pi }{4}\]

    C) \[n\pi +{{(-1)}^{n}}\frac{\pi }{3}\]                            

    D) \[n\pi +{{(-1)}^{n}}\frac{\pi }{4}\]

    Correct Answer: C

    Solution :

    We have,\[2\sqrt{3}\cos \theta =\tan \theta \] \[\Rightarrow \]               \[2\sqrt{3}\cos \theta =\frac{\sin \theta }{\cos \theta }\] \[\Rightarrow \]               \[2\sqrt{3}{{\cos }^{2}}\theta =\sin \theta \] \[\Rightarrow \]               \[2\sqrt{3}{{\sin }^{2}}\theta +\sin \theta -2\sqrt{3}=0\] \[\Rightarrow \]               \[\sin \theta =\frac{-1\pm 7}{4\sqrt{3}}\] \[\Rightarrow \]               \[\sin \theta =\frac{-8}{4\sqrt{3}}\](impossible) \[\therefore \]  \[\sin \theta =\frac{6}{4\sqrt{3}}=\frac{\sqrt{3}}{2}\] \[\Rightarrow \]               \[\theta =n\pi +{{(-1)}^{n}}\frac{\pi }{3}\]


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