J & K CET Engineering J and K - CET Engineering Solved Paper-2007

  • question_answer
    If the centroid of the triangle formed by the points \[(0,\,0),\,\,(\cos \theta ,\sin \theta )\] and \[(sin\theta ,-\cos \theta )\] lies on the line \[y=2x,\]then \[\theta \] is equal to

    A)  \[{{\tan }^{-1}}\,\,2\]       

    B)  \[{{\tan }^{-1}}\,\,3\]

    C)  \[{{\tan }^{-1}}\,\,(-3)\]   

    D)  \[{{\tan }^{-1}}\,\,(-2)\]

    Correct Answer: C

    Solution :

    Given vertices of triangle are \[O(0,0),\] \[A(\cos \theta ,\,\sin \theta )\] and \[B(sin\theta ,\,-cos\,\theta )\] coordinate of centroid are \[\left( \frac{\cos \,\theta +\sin \theta }{3},\,\,\frac{\sin \theta -\cos \theta }{3} \right)\]. Since, centroid lies on the line \[y=2x.\] \[\therefore \]    \[\frac{\sin \theta -\cos \theta }{3}=\frac{2\,\cos \theta +2\sin \theta }{3}\] \[\Rightarrow \] \[\sin \theta =-3\cos \theta \] \[\Rightarrow \] \[\tan \theta =-3\] \[\Rightarrow \] \[\theta ={{\tan }^{-1}}(-3)\]


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