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

  • question_answer
    The equation of the image of circle \[{{x}^{2}}+{{y}^{2}}+16x-24y+183=0\] by the line mirror \[4x+7y+13=0\] is

    A) \[{{x}^{2}}+{{y}^{2}}+32x-4y+235=0\]

    B) \[{{x}^{2}}+{{y}^{2}}+32x+4y-235=0\]

    C) \[{{x}^{2}}+{{y}^{2}}+32x-4y-235=0\]

    D) \[{{x}^{2}}+{{y}^{2}}+32x+4y+235=0\]

    Correct Answer: D

    Solution :

    [d] The centre of the given circle is \[(-8,12)\] and radius is 5. The image of the circle will have the same radius, i.e. the radius of the required circle is 5. The centre D of the required circle is the image of the centre C of the given circle in the line mirror. If D be \[(\alpha ,\beta )\] then \[\frac{\alpha +8}{4}=\frac{\beta -12}{7}=-2\left[ \frac{4\times -8+7\times 12+13}{{{4}^{2}}+{{7}^{2}}} \right]\] [See straight line] Or, \[\frac{\alpha +8}{4}=\frac{\beta -12}{7}=\frac{-2\times 65}{65}=-2\] \[\therefore \,\,\,\,\,\,\alpha =-16,\,\,\beta =-2\] \[\therefore \] Required circle is \[{{(x+16)}^{2}}+{{(y+2)}^{2}}={{5}^{2}}\]


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