JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Tangent and normal to a circle

  • question_answer
    The equations of the normals to the circle \[{{x}^{2}}+{{y}^{2}}-8x-2y+12=0\]at the points whose ordinate is  ?1, will be

    A)            \[2x-y-7=0,\,2x+y-9=0\]      

    B)            \[2x+y+7=0,\,2x+y+9=0\]

    C)            \[2x+y-7=0,\,\,2x+y+9=0\]

    D)            \[2x-y+7=0,\,2x-y+9=0\]

    Correct Answer: A

    Solution :

               The abscissa of point is found by substituting the ordinates and solving for abscissa.                    \[\Rightarrow {{x}^{2}}-8x+15=0\]                    \[\Rightarrow x=\frac{8\pm \sqrt{64-60}}{2}=\frac{8\pm 2}{2}=5\] or 3                    i.e., points are \[(5,\ -1)\]and (3,?1).                    Normal is given by, \[\frac{x-5}{5-4}=\frac{y+1}{-1-1}\Rightarrow 2x+y-9=0\]                    and \[\frac{x-3}{3-4}=\frac{y+1}{-1-1}\Rightarrow 2x-y-7=0\].


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