JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2005

  • question_answer
        The two curves\[{{x}^{3}}-3x{{y}^{2}}+2=0\]and\[3{{x}^{2}}y-{{y}^{3}}-2=0\]:

    A)  cut at right angles

    B)  touch each other

    C)  cut at an angle\[\frac{\pi }{3}\]

    D)  cut at an angle\[\frac{\pi }{4}\]

    Correct Answer: A

    Solution :

                    We have\[{{x}^{3}}-3x{{y}^{2}}+2=0\]            ...(i) and       \[3{{x}^{2}}y-{{y}^{3}}-2=0\]                    ...(ii) Diff. equation (i) and (ii) with respect to\[x,\]we obtain \[{{\left( \frac{dy}{dx} \right)}_{{{C}_{1}}}}=\frac{{{x}^{2}}-{{y}^{2}}}{2xy}\]and\[{{\left( \frac{dy}{dx} \right)}_{C2}}=\frac{-2xy}{{{x}^{2}}-{{y}^{2}}}\]                 \[{{m}_{1}}\times {{m}_{2}}=-1\] Hence, the two curves cut at right angles.


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