JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        The eccentricity of the conic represented by \[{{x}^{2}}-{{y}^{2}}-4x+4y+16=0\]is

    A)  1                                            

    B)  \[\sqrt{2}\]

    C)  2                                            

    D)  \[1/2\]

    Correct Answer: B

    Solution :

                    We have,\[{{x}^{2}}-{{y}^{2}}-4x+4y+16=0\] \[\Rightarrow \]               \[({{x}^{2}}-4x)-({{y}^{2}}-4y)=-16\] \[\Rightarrow \]\[({{x}^{2}}-4x+4)-({{y}^{2}}-4y+4)=-16\]             \[\Rightarrow \]               \[{{(x-2)}^{2}}-{{(y-2)}^{2}}=-16\] \[\Rightarrow \]               \[\frac{{{(x-2)}^{2}}}{{{4}^{2}}}-\frac{{{(y-2)}^{2}}}{{{4}^{2}}}=1\] Shifting the origin at (2, 2), we get \[\frac{{{X}^{2}}}{{{4}^{2}}}-\frac{{{Y}^{2}}}{{{4}^{2}}}=-1\]where \[x=X+2,\text{ }y=Y+2\] This is a rectangular hyperbola, whose eccentricity is always\[\sqrt{2}\].


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