JEE Main & Advanced Mathematics Conic Sections Question Bank Ellipse

  • question_answer
    The equation of the normal at the point (2, 3) on the ellipse \[9{{x}^{2}}+16{{y}^{2}}=180\], is        [MP PET 2000]

    A)            \[3y=8x-10\]                             

    B)            \[3y-8x+7=0\]

    C)            \[8y+3x+7=0\]                           

    D)            \[3x+2y+7=0\]

    Correct Answer: B

    Solution :

               \[\frac{x-{{x}_{1}}}{{{x}_{1}}/{{a}^{2}}}=\frac{y-{{y}_{1}}}{{{y}_{1}}/{{b}^{2}}}\], which is the standard equation of normal at point \[({{x}_{1}},\,{{y}_{1}})\].            In the given ellipse, \[{{a}^{2}}=20,\,{{b}^{2}}=\frac{180}{16}\].                    Hence the equation of normal at the point \[(2,\,3)\] is                    \[\frac{x-2}{2/20}=\frac{y-3}{48/180}\] Þ \[40\,(x-2)=15(y-3)\]                    Þ \[8x-3y=7\]Þ \[3y-8x+7=0\].


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