JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Equations of circle, Geometrical problems regarding circle

  • question_answer
    The locus of the centre of a circle which touches externally the circle \[{{x}^{2}}+{{y}^{2}}-6x-6y+14=0\] and also touches the y-axis, is given by the equation                                 [IIT 1993; DCE 2000]

    A)            \[{{x}^{2}}-6x-10y+14=0\]     

    B)            \[{{x}^{2}}-10x-6y+14=0\]

    C)            \[{{y}^{2}}-6x-10y+14=0\]     

    D)            \[{{y}^{2}}-10x-6y+14=0\]

    Correct Answer: D

    Solution :

               Let the centre be (h, k), then radius = h                    Also \[C{{C}_{1}}={{R}_{1}}+{{R}_{2}}\]                    or \[\sqrt{{{(h-3)}^{2}}+{{(k-3)}^{2}}}=h+\sqrt{9+9-14}\]                    \[\Rightarrow {{(h-3)}^{2}}+{{(k-3)}^{2}}={{h}^{2}}+4+4h\]                    \[\Rightarrow {{k}^{2}}-10h-6k+14=0\] or \[{{y}^{2}}-10x-6y+14=0\].


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