JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    If\[2-{{\cos }^{2}}\theta =3\sin \theta \cos \theta \],\[\sin \theta \ne cos\theta \], then find the value of\[\cot \theta \]

    A) \[\frac{1}{2}\]                                   

    B) \[0\]

    C) \[-1\]                                    

    D) \[2\]

    Correct Answer: D

    Solution :

    \[2-{{\cos }^{2}}\theta =3\sin \theta \cos \theta \] Dividing both sides by\[{{\cos }^{2}}\theta \], we get                         \[2{{\sec }^{2}}\theta -1=3\tan \theta \]                 \[2(1+{{\tan }^{2}}\theta )-1=3\tan \theta \] \[\Rightarrow \]               \[2+2{{\tan }^{2}}\theta -1=3\tan \theta \] \[\Rightarrow \]               \[2{{\tan }^{2}}\theta -3\tan \theta +1=0\] \[\Rightarrow \]               \[2{{\tan }^{2}}\theta -2\tan \theta -\tan \theta +1=0\] \[\Rightarrow \]               \[2\tan \theta (\tan \theta -1)-(\tan \theta -1)=0\] \[\Rightarrow \]               \[(2\tan \theta -1)(\tan \theta -1)=0\] \[\Rightarrow \]               \[\tan \theta =\frac{1}{2}\]and\[1\] \[\Rightarrow \]               \[\cot \theta =2\]and\[1\]


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