JEE Main & Advanced Sample Paper JEE Main Sample Paper-16

  • question_answer
    The   common   tangent   between\[~9{{x}^{2}}-16\text{ }{{y}^{2}}=144\]and \[~{{x}^{2}}+{{y}^{2}}=9\]cuts the coordinate axes at A and B, then the product OA-OB equals

    A) \[\frac{75}{\sqrt{7}}\]                                   

    B) \[\frac{150}{\sqrt{7}}\]

    C) \[\frac{75}{\sqrt{14}}\]                 

    D)  None of these

    Correct Answer: C

    Solution :

    Tangent to\[9{{x}^{2}}-16{{y}^{2}}=144\]is \[y=mx\pm \sqrt{16{{m}^{2}}-9}.\] Since it touches circle also \[\therefore \]  \[\frac{\sqrt{16{{m}^{2}}-9}}{\sqrt{1+{{m}^{2}}}}=3\]or\[16{{m}^{2}}-9=9+9{{m}^{2}}\]or\[{{m}^{2}}=\frac{18}{7}\]Equation of tangent \[y=\pm 3\sqrt{\frac{2}{7}}x\pm \frac{15}{\sqrt{7}}\]


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