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

  • question_answer
    If the curve \[y={{a}^{x}}\] and \[y={{b}^{x}}\] intersect at angle \[\alpha \] then,\[\tan \alpha =\]                                     [MP PET 2001]

    A)            \[\frac{a-b}{1+ab}\]

    B)            \[\frac{\log a-\log b}{1+\log a\log b}\]

    C)            \[\frac{a+b}{1-ab}\]

    D)            \[\frac{\log a+\log b}{1-\log a\log b}\]

    Correct Answer: B

    Solution :

               Clearly the point of intersection of curves is (0, 1). Now, slope of tangent of first curve \[{{m}_{1}}=\frac{dy}{dx}={{a}^{x}}\log a\]            Þ \[{{\left( \frac{dy}{dx} \right)}_{(0,\,1)}}={{m}_{1}}=\log a\]            Slope of tangent of second curve \[{{m}_{2}}=\frac{dy}{dx}={{b}^{x}}\log b\]            Þ \[{{m}_{2}}={{\left( \frac{dy}{dx} \right)}_{(0,\,1)}}=\log b\]            \ \[\tan \alpha =\frac{{{m}_{1}}-{{m}_{2}}}{1+{{m}_{1}}{{m}_{2}}}=\frac{\log a-\log b}{1+\log a\log b}\].


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