JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The equation of the parabola with focus (a, b) and directrix \[\frac{x}{a}+\frac{y}{b}=1\] is given by               [MP PET 1997]

    A)            \[{{(ax-by)}^{2}}-2{{a}^{3}}x-2{{b}^{3}}y+{{a}^{4}}+{{a}^{2}}{{b}^{2}}+{{b}^{4}}=0\]

    B)            \[{{(ax+by)}^{2}}-2{{a}^{3}}x-2{{b}^{3}}y-{{a}^{4}}+{{a}^{2}}{{b}^{2}}-{{b}^{4}}=0\]

    C)            \[{{(ax-by)}^{2}}+{{a}^{4}}+{{b}^{4}}-2{{a}^{3}}x=0\]

    D)            \[{{(ax-by)}^{2}}-2{{a}^{3}}x=0\]

    Correct Answer: A

    Solution :

               \[{{(x-a)}^{2}}+{{(y-b)}^{2}}={{\left( \frac{bx+ay-ab}{\sqrt{{{a}^{2}}+{{b}^{2}}}} \right)}^{2}}\]            On solving we get            \[{{(ax-by)}^{2}}-2{{a}^{3}}x-2{{b}^{3}}y+{{a}^{4}}+{{a}^{2}}{{b}^{2}}+{{b}^{4}}=0\].


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