JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2011

  • question_answer
        If\[{{m}_{1}}\]and\[{{m}_{2}}\]are the slopes of the tangents to the hyperbola\[\frac{{{x}^{2}}}{25}-\frac{{{y}^{2}}}{16}=1\]which pass through the point (6, 2), then

    A)  \[{{m}_{1}}+{{m}_{2}}=-\frac{24}{11}\]

    B)  \[{{m}_{1}}{{m}_{2}}=\frac{20}{11}\]

    C)  \[{{m}_{1}}+{{m}_{2}}=\frac{48}{11}\]  

    D)  \[{{m}_{1}}{{m}_{2}}=\frac{11}{20}\]

    Correct Answer: B

    Solution :

                    The equation of a line passing through (6, 2) is \[y-2=m(x-6)\] \[\Rightarrow \]               \[y=mx+2-6m\] Since, this line is tangent to the given hyperbola. \[\therefore \] \[{{(2-6m)}^{2}}=25{{m}^{2}}-16\] \[\Rightarrow \]               \[36{{m}^{2}}+4-24m-25{{m}^{2}}+16=0\] \[\Rightarrow \]               \[11{{m}^{2}}-24m+20=0\] Let\[{{m}_{1}}\]and\[{{m}_{2}}\]are the roots of the above equation. \[\therefore \]  \[{{m}_{1}}+{{m}_{2}}=\frac{24}{11}\]and \[{{m}_{1}}{{m}_{2}}=\frac{20}{11}\]


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