KVPY Sample Paper KVPY Stream-SX Model Paper-6

  • question_answer
    Tangent at (0, 0), to the curve \[{{y}^{2}}={{x}^{3}}+{{x}^{2}}\]

    A) touches X-axis

    B) bisects the angle between the axes

    C) makes an angle of \[60{}^\circ \] with OX

    D) none of these

    Correct Answer: B

    Solution :

    \[{{y}^{2}}={{x}^{2}}\,(x+1),\]                    \[x+1\ge 0\]
    \[y=\pm \,\,x\sqrt{x+1}\]
    \[\therefore \]      \[\frac{dy}{dx}=\pm \left( \sqrt{x+1}+\frac{x}{2\sqrt{x+1}} \right)\]
                \[=\pm \,\,\frac{2\,(x+1)+x}{2\sqrt{x+1}}=\pm \,\,\frac{3x+2}{2\sqrt{x+1}}\]
    \[\therefore \]      \[\underset{x\,=\,0}{\mathop{\left. \frac{dy}{dx} \right|}}\,=\pm \,\,1\]
    \[\therefore \]      at (0, 0) the curve bisects the angle between the axes.


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