JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The ordinates of the triangle inscribed in parabola \[{{y}^{2}}=4ax\] are \[{{y}_{1}},\ {{y}_{2}},\ {{y}_{3}}\], then the area of triangle is

    A)            \[\frac{1}{8a}({{y}_{1}}+{{y}_{2}})({{y}_{2}}+{{y}_{3}})({{y}_{3}}+{{y}_{1}})\]

    B)            \[\frac{1}{4a}({{y}_{1}}+{{y}_{2}})({{y}_{2}}+{{y}_{3}})({{y}_{3}}+{{y}_{1}})\]

    C)            \[\frac{1}{8a}({{y}_{1}}-{{y}_{2}})({{y}_{2}}-{{y}_{3}})({{y}_{3}}-{{y}_{1}})\]

    D)            \[\frac{1}{4a}({{y}_{1}}-{{y}_{2}})({{y}_{2}}-{{y}_{3}})({{y}_{3}}-{{y}_{1}})\]

    Correct Answer: B

    Solution :

               Points \[\left( \frac{y_{1}^{2}}{4a},{{y}_{1}} \right),\,\left( \frac{y_{2}^{2}}{4a},{{y}_{2}} \right),\,\,\left( \frac{y_{3}^{2}}{4a},{{y}_{3}} \right)\]            Use area formula and get       \[\Delta =\frac{1}{8a}({{y}_{1}}-{{y}_{2}})({{y}_{2}}-{{y}_{3}})({{y}_{3}}-{{y}_{1}})\].


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