CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2009

  • question_answer
    The sum of the distances of a point\[(2,-3)\]from the foci of an ellipse\[16{{(x-2)}^{2}}+25({{y}^{4}}-\] \[3{{)}^{2}}=400\]is

    A)  8                                            

    B)  6

    C)  50                         

    D)         32

    E)  10

    Correct Answer: B

    Solution :

    Given equation of ellipse can be rewritten as \[\frac{{{(x-2)}^{2}}}{25}+\frac{{{(y+3)}^{2}}}{16}=1\] \[\Rightarrow \]               \[\frac{{{X}^{2}}}{25}+\frac{{{Y}^{2}}}{16}=1\] Where \[X=x-2,Y=y+3\] Here, \[a>b\] \[\therefore \]  \[e=\sqrt{1-\frac{{{b}^{2}}}{{{a}^{2}}}}=\sqrt{1-\frac{16}{25}}=\frac{3}{5}\] \[\therefore \]  Focus\[(\pm ae,0)=(\pm \text{ }3,0)\] \[\Rightarrow \]      \[x-2=\pm \text{ }3,\text{ }y+3=0\] \[\Rightarrow \]               \[x=5,-1,\text{ }y=-3\] \[\therefore \]Foci are\[(-1,-3)\]and\[(5,-3)\]. Distance between\[(2,-3)\]and\[(-1,-3)\] \[=\sqrt{{{(2+1)}^{2}}+{{(-3+3)}^{2}}}=3\] and distance between\[(2,-3)\]and\[(5,-3)\] \[=\sqrt{{{(2-5)}^{2}}+{{(-3+3)}^{2}}}=3\] Hence, sum of the distance of point\[(2,-3)\] from the foci\[=3+3=6\]


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