JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        The  equation  of\[f\]those  tangents  to \[4{{x}^{2}}-9{{y}^{2}}=36\]which are perpendicular to the straight line\[5x+2y-10=0\]are

    A)  \[5(y-3)=2\left( x-\frac{\sqrt{117}}{2} \right)\]

    B)  \[2x-5y+10-2\sqrt{18}=0\]

    C)  \[2x-5y-10-2\sqrt{18}=0\]

    D)  None of the above

    Correct Answer: D

    Solution :

                    \[4{{x}^{2}}-9{{y}^{2}}=36\] On differentiating w.r.t.\[x,\]we get \[\Rightarrow \]               \[8x-18y\frac{dy}{dx}=0\] \[\Rightarrow \]                               \[\frac{dy}{dx}=\frac{4x}{9y}\] Slope of the tangent\[=\frac{4x}{9y}\] \[\therefore \]For this tangent to be perpendicular to the straight line\[5x+2y-10=0,\] we must have                 \[\frac{4x}{9y}\times \frac{5}{-2}=-1\] \[\Rightarrow \]               \[y=\frac{10x}{9}\] Putting this value of y in\[4{{x}^{2}}-9{{y}^{2}}=36,\]we get \[-64{{x}^{2}}=324,\]which does not have real roots. Hence, at no points on the given curve can the tangent be perpendicular to given line.


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