JEE Main & Advanced JEE Main Paper Phase-I (Held on 08-1-2020 Morning)

  • question_answer
    Let the line y = mx and the ellipse \[2{{x}^{2}}+{{y}^{2}}=1\]intersect at a point P in the first quadrant. If the normal to this ellipse at P meets the co-ordinate axes at \[\left( -\frac{1}{3\sqrt{2}},0 \right)\] and \[(0,\beta )\], then \[\beta \] is equal to     [JEE MAIN Held On 08-01-2020 Morning]

    A) \[\frac{\sqrt{2}}{3}\]

    B) \[\frac{2}{3}\]

    C) \[\frac{2}{\sqrt{3}}\]

    D) \[\frac{2\sqrt{2}}{3}\]

    Correct Answer: A

    Solution :

    Let P (a, b) then equation of normal at P is \[\frac{x}{2a}-\frac{y}{b}=\frac{-1}{2}\] \[\downarrow \left( \frac{-1}{3\sqrt{2}},0 \right)\] \[\Rightarrow \frac{-1}{6\sqrt{2a}}=\frac{-1}{2}\Rightarrow a=\frac{1}{3\sqrt{2}}\] also \[2{{a}^{2}}+{{b}^{2}}=1\] we get \[{{b}^{2}}=1-2\times \frac{1}{18}=\frac{8}{9}\Rightarrow b=\frac{2\sqrt{2}}{3}\] Hence normal is \[\frac{3\sqrt{2x}}{2}-\frac{3y}{2\sqrt{2}}=\frac{-1}{2}\] \[\downarrow (0,\beta )\] \[\beta =\frac{\sqrt{2}}{3}\]      


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