JCECE Engineering JCECE Engineering Solved Paper-2015

  • question_answer
    If the axes are rotated through an angle of \[{{30}^{o}}\] in the clockwise direction, the point \[(4,\,\,2\sqrt{3})\] in the new system is

    A) \[(2,\,\,3)\]

    B)  \[(2,\,\,\sqrt{3})\]

    C)  \[(\sqrt{3},\,\,2)\]

    D)  \[(\sqrt{3},\,\,5)\]

    Correct Answer: D

    Solution :

    We have, \[x=4,\,\,y=2\sqrt{3}\] and\[\theta =-{{30}^{o}}\] \[\therefore \]  \[X=x\cos \theta +y\sin \theta \] and        \[Y=-x\sin \theta +y\cos \theta \] \[\Rightarrow \]               \[X=4\cos {{30}^{o}}-2\sqrt{3}\sin {{30}^{o}}\]                 \[=4\times \frac{\sqrt{3}}{2}-2\sqrt{3}\times \frac{1}{2}\] and        \[Y=4\sin {{30}^{o}}+2\sqrt{3}\cos {{30}^{o}}\]                 \[=4\times \frac{1}{2}+2\sqrt{3}\times \frac{\sqrt{3}}{2}\] \[\Rightarrow \]               \[X=\sqrt{3}\]and\[Y=5\] Hence, the given point in the new system is\[(\sqrt{3},\,5)\].


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