CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

  • question_answer
    The centroid of a triangle formed by the points (0, 0),\[(cos\text{ }\theta ,\text{ }sin\text{ }\theta )\]and\[(sin\text{ }\theta -cos\text{ }\theta )\]lie on the line\[y=2x;\]then\[\theta \]is:

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

    B)  \[{{\tan }^{-1}}\frac{1}{3}\]       

    C)         \[{{\tan }^{-1}}\frac{1}{2}\]       

    D)         \[{{\tan }^{-1}}(-2)\]

    E)  \[{{\tan }^{-1}}(-3)\]

    Correct Answer: E

    Solution :

    Centroid of a triangle whose vertices are (0,0), \[(\cos \theta ,\sin \theta )\]and\[(\sin \theta ,-\cos \theta )\]is \[\left( \frac{\cos \theta +\sin \theta }{3},\frac{\sin \theta -\cos \theta }{3} \right)\] But centroid lies on a line\[y=2x\] \[\therefore \]  \[\frac{-\cos \theta +\sin \theta }{3}=\frac{2(\sin \theta +\cos \theta )}{3}\] \[\Rightarrow \]               \[-3\cos \theta =\sin \theta \] \[\Rightarrow \]               \[\tan \theta =-3\] \[\Rightarrow \]               \[\theta ={{\tan }^{-1}}(-3)\]


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