JEE Main & Advanced Mathematics Conic Sections Question Bank Self Evaluation Test - Conic Sections

  • question_answer
    The length of the chord intercepted by the circle \[{{x}^{2}}+{{y}^{2}}={{r}^{2}}\] on the line \[\frac{x}{a}+\frac{y}{b}=1\] is

    A) \[\sqrt{\frac{{{r}^{2}}({{a}^{2}}+{{b}^{2}})-{{a}^{2}}{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}}}\]

    B) \[2\sqrt{\frac{{{r}^{2}}({{a}^{2}}+{{b}^{2}})-{{a}^{2}}{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}}}\]

    C) \[2\frac{\sqrt{{{r}^{2}}({{a}^{2}}+{{b}^{2}})-{{a}^{2}}{{b}^{2}}}}{{{a}^{2}}+{{b}^{2}}}\]

    D) None of these

    Correct Answer: B

    Solution :

    [b] Length of chord \[=2{{\{{{(radius)}^{2}}-{{(length\,\,of\bot from\,\,centre\,\,of\,\,chord)}^{2}}\}}^{1/2}}\]\[=2{{\left\{ {{r}^{2}}-{{\left( \frac{-1}{\sqrt{(1/{{a}^{2}})+(1/{{b}^{2}})}} \right)}^{2}} \right\}}^{1/2}}\] \[=2\sqrt{\frac{{{r}^{2}}({{a}^{2}}+{{b}^{2}})-{{a}^{2}}{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}}}\]


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