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

  • question_answer
    The equation of the tangent to curve \[y=b{{e}^{-x/a}}\] at the point where it crosses y-axis is                             [Karnataka CET 2002]

    A)             \[ax+by=1\]

    B)             \[ax-by=1\]

    C)            \[\frac{x}{a}-\frac{y}{b}=1\]

    D)            \[\frac{x}{a}+\frac{y}{b}=1\]

    Correct Answer: D

    Solution :

               Curve is \[y=b{{e}^{-x/a}}\]            Since the curve crosses y-axis (i.e., x = 0) \ \[y=b\]            Now \[\frac{dy}{dx}=\frac{-b}{a}{{e}^{-x/a}}\]. At point (0, b),\[{{\left( \frac{dy}{dx} \right)}_{(0,\,b)}}=\frac{-b}{a}\]            \Equation of tangent is, \[y-b=\frac{-b}{a}(x-0)\]            \[\Rightarrow \]\[\frac{x}{a}+\frac{y}{b}=1\].


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