JEE Main & Advanced JEE Main Paper (Held on 7 May 2012)

  • question_answer
    If the eccentricity of a hyperbola \[\frac{{{x}^{2}}}{9}-\frac{{{y}^{2}}}{{{b}^{2}}}=1,\]which passes through (k, 2), is \[\frac{\sqrt{13}}{3},\] then the value of \[{{k}^{2}}\] is   JEE Main Online Paper (Held On 07 May 2012)

    A) 18  

    B)                        8

    C)                        1                                             

    D)                        2

    Correct Answer: A

    Solution :

                    Given hyperbola is\[\frac{{{x}^{2}}}{9}-\frac{{{y}^{2}}}{{{b}^{2}}}=1\] \[\frac{{{K}^{2}}}{9}-\frac{4}{{{b}^{2}}}=1\]                                                         ?(1) Also, given\[e=\sqrt{1+\frac{{{b}^{2}}}{{{a}^{2}}}}=\frac{\sqrt{13}}{3}\] \[\Rightarrow \]\[\sqrt{1+\frac{{{b}^{2}}}{9}}=\frac{\sqrt{13}}{3}\Rightarrow 9+{{b}^{2}}=13\]\[\Rightarrow \]\[b=\pm 2\] Now, from \[e{{q}^{n}}(1),\]we have \[\frac{{{K}^{2}}}{9}-\frac{4}{4}=1\]         \[(\because b=\pm 2)\]\[\Rightarrow \]\[{{K}^{2}}=18\]                                


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