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

  • question_answer
    The point of the curve \[{{y}^{2}}=2(x-3)\] at which the normal is parallel to the line\[y-2x+1=0\]is           [MP PET 1998]

    A)             (5,2)

    B)            \[\left( -\frac{1}{2},-2 \right)\]

    C)            (5, ?2)

    D)            \[\left( \frac{3}{2},\,2 \right)\]

    Correct Answer: C

    Solution :

                       Given \[{{y}^{2}}=2(x-3)\]                         .....(i)            Differentiate w.r.t. x, \[2y.\frac{dy}{dx}=2\Rightarrow \frac{dy}{dx}=\frac{1}{y}\]            Slope of the normal \[=\frac{-1}{\left( \frac{dy}{dx} \right)}=-y\]            Slope of the given line \[=2\]            \[\therefore y=-2\]            From equation (i), \[x=5\]            \[\therefore \]Required point is \[(5,\,-2)\].


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