CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    A conic section is defined by the equations\[x=-1+\sec t,\text{ }y=2+3\text{ }tan\text{ }t\]. The coordinates of the foci are

    A)  \[(-1-\sqrt{10},2)\]and \[(-1+\sqrt{10},2)\]

    B)  \[(-1-\sqrt{8},2)\]and \[(-1+\sqrt{8},2)\]

    C)  \[(-1,2-\sqrt{8})\]and \[(-1,2+\sqrt{8})\]

    D)  \[(-1,2-\sqrt{10})\]and \[(-1,2+\sqrt{10})\]

    E)  \[(\sqrt{10},0)\]and \[(-\sqrt{10},0)\]

    Correct Answer: A

    Solution :

    Given equations can be rewritten as \[x+1=\sec t,\frac{y-2}{3}=\tan t\] Since, \[{{\sec }^{2}}t-{{\tan }^{2}}t=1\] \[\therefore \]  \[\frac{{{(x+1)}^{2}}}{1}-\frac{{{(y-2)}^{2}}}{9}=1\] Now, \[e=\sqrt{1+\frac{{{b}^{2}}}{{{a}^{2}}}}=\sqrt{1+\frac{9}{1}}=\sqrt{10}\] \[\therefore \]  \[Foci=(-1\pm ae,2)\]                 \[=(-1-\sqrt{10},2)\]and\[(-1+\sqrt{10},2)\]


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