JEE Main & Advanced Sample Paper JEE Main Sample Paper-22

  • question_answer
    If a curve passing through (1, 1) is such that the tangent drawn at any point P on it intersects the \[x\] -axis at Q and the reciprocal of abscissa of point P is equal to twice \[x\]  -intercept of tangent at P. Then the equation of the curve is

    A)  \[{{y}^{2}}=x\]                    

    B)  \[{{x}^{2}}=2y-1\]

    C)  \[3{{x}^{2}}-2{{y}^{2}}=1\]           

    D)  \[2{{x}^{2}}-{{y}^{2}}=1\]

    Correct Answer: D

    Solution :

    \[2\left( x-\frac{y}{\frac{dy}{dx}} \right)\,=\frac{1}{x}\] \[x-\frac{1}{2x}=\frac{y}{\frac{dy}{dx}}\Rightarrow \,\frac{(2{{x}^{2}}-1)}{2x}=\frac{y}{\frac{dy}{dx}}\] \[\int_{{}}^{{}}{\frac{dy}{y}\,=\int_{{}}^{{}}{\frac{2x}{(2{{x}^{2}}-1)}dx}}\] so \[y=k{{(2{{x}^{2}}-1)}^{1/2}}\] Here, k = 1 thus \[{{y}^{2}}=2{{x}^{2}}-1\]\[2{{x}^{2}}-{{y}^{2}}=1\]


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