KVPY Sample Paper KVPY Stream-SX Model Paper-12

  • question_answer
    The line \[2px+y\sqrt{1-{{p}^{2}}}=1(\left| p \right|<1)\] for different value of \[p,\]touches

    A) An ellipse of eccentricity\[\frac{2}{\sqrt{3}}\]

    B) An ellipse of eccentricity \[\frac{\sqrt{3}}{2}\]

    C) Hyperbola of eccentricity 2

    D) A hyperbola of eccentricity \[\sqrt{2}\]

    Correct Answer: B

    Solution :

    \[y=\frac{-2p}{\sqrt{1-{{p}^{2}}}}\operatorname{x}+\frac{1}{\sqrt{1-{{p}^{2}}}};m=\frac{-2p}{\sqrt{1-{{p}^{2}}}}\]
    \[\Rightarrow \]\[{{m}^{2}}=\frac{4{{p}^{2}}}{1-{{p}^{2}}}\Rightarrow {{m}^{2}}=(4+{{m}^{2}}){{p}^{2}}\]
    \[\Rightarrow \]\[{{p}^{2}}=\frac{{{m}^{2}}}{4+{{m}^{2}}}\]
    \[y=mx+\frac{1}{\sqrt{1-\frac{{{m}^{2}}}{4+{{m}^{2}}}}}\]
    \[\Rightarrow \]\[y=mx+\sqrt{\frac{4+{{m}^{2}}}{4}}\]
    \[\Rightarrow \]\[y=mx+\sqrt{1+\frac{1}{4}{{m}^{2}}}\]
    Which touches the ellipse \[\frac{{{x}^{2}}}{1/4}+\frac{{{y}^{2}}}{1}=1\]
    Whose eccentricity\[e=\sqrt{1-\frac{1}{4}}=\frac{\sqrt{3}}{2}\]


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