JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Tangent and Normal

  • question_answer
    The angle of intersection of the curves \[y={{x}^{2}}\] and \[x={{y}^{2}}\] at (1, 1) is [Roorkee 2000; Karnataka CET 2001]

    A)            \[{{\tan }^{-1}}\left( \frac{4}{3} \right)\]

    B)            \[{{\tan }^{-1}}(1)\]

    C)            \[{{90}^{o}}\]

    D)            \[{{\tan }^{-1}}\left( \frac{3}{4} \right)\]

    Correct Answer: D

    Solution :

               \[y={{x}^{2}}\] Þ \[\frac{dy}{dx}={{m}_{1}}=2x\]            Þ  \[{{\left( \frac{dy}{dx} \right)}_{(1,\,1)}}=2={{m}_{1}}\] and \[x={{y}^{2}}\] Þ \[1=2y\,\frac{dy}{dx}\]            Þ  \[\frac{dy}{dx}={{m}_{2}}=\frac{1}{2y}\] Þ \[{{\left( \frac{dy}{dx} \right)}_{(1,\,1)}}=\frac{1}{2}\]            \[\therefore \]Angle of intersection, \[\tan \theta =\frac{{{m}_{1}}-{{m}_{2}}}{1+{{m}_{1}}{{m}_{2}}}\]=\[\frac{2-\frac{1}{2}}{1+2\times \frac{1}{2}}\]=\[\frac{3}{4}\]            Þ\[\theta ={{\tan }^{-1}}(3/4)\].


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