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

  • question_answer
    The equation of the circle with centre on x-axis, radius 5 and passing through the point (2, 3), is

    A)            \[{{x}^{2}}+{{y}^{2}}+4x-21=0\]                                  

    B)            \[{{x}^{2}}+{{y}^{2}}+4x+21=0\]

    C)            \[{{x}^{2}}+{{y}^{2}}-4x-21=0\]                                    

    D)            \[{{x}^{2}}+{{y}^{2}}+5x-21=0\]

    Correct Answer: A

    Solution :

               Let centre be\[(-g,\ 0)\], then \[\sqrt{{{g}^{2}}-c}=5\Rightarrow c={{g}^{2}}-25\]                    Also it passes through (2, 3), therefore                    \[13+4g+{{g}^{2}}-25=0\Rightarrow g=-6,\ 2\]                    Hence the equations are \[{{x}^{2}}+{{y}^{2}}-12x+11=0\] and \[{{x}^{2}}+{{y}^{2}}+4x-21=0\]. 


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