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

  • question_answer
    The centre of a circle is (2, ?3) and the circumference is \[10\pi \]. Then the equation of the circle is [Kerala (Engg.) 2002]

    A)            \[{{x}^{2}}+{{y}^{2}}+4x+6y+12=0\]                        

    B)            \[{{x}^{2}}+{{y}^{2}}-4x+6y+12=0\]

    C) \[{{x}^{2}}+{{y}^{2}}-4x+6y-12=0\]                                       

    D)            \[{{x}^{2}}+{{y}^{2}}-4x-6y-12=0\]

    Correct Answer: C

    Solution :

               Centre (2, ? 3)                                         Circumference \[=10\pi \,\]Þ \[2\pi r=10\pi \]Þ \[r=5.\]                    From\[{{(x-h)}^{2}}+{{(y-k)}^{2}}={{r}^{2}}\],                    \[{{(x-2)}^{2}}+{{(y+3)}^{2}}={{5}^{2}}\]                    Þ \[{{x}^{2}}+{{y}^{2}}-4x+6y+13=25\]                    Þ \[{{x}^{2}}+{{y}^{2}}-4x+6y-12=0\],                    which is the required equation of the circle.


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