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 which touches both axes and whose centre is \[({{x}_{1}},\ {{y}_{1}})\] is                                   [MP PET 1988]

    A)            \[{{x}^{2}}+{{y}^{2}}+2{{x}_{1}}(x+y)+x_{1}^{2}=0\]

    B)            \[{{x}^{2}}+{{y}^{2}}-2{{x}_{1}}(x+y)+x_{1}^{2}=0\]

    C)            \[{{x}^{2}}+{{y}^{2}}=x_{1}^{2}+y_{1}^{2}\]     

    D)            \[{{x}^{2}}+{{y}^{2}}+2x{{x}_{1}}+2y{{y}_{1}}=0\]

    Correct Answer: B

    Solution :

               The equation will be                    \[{{(x-{{x}_{1}})}^{2}}+{{(y-{{y}_{1}})}^{2}}={{r}^{2}}\]                    As the circle touches both the axes, \[(r)=\sqrt{{{(4)}^{2}}+{{(3)}^{2}}}=5\]                    \ \[{{(x-{{x}_{1}})}^{2}}+{{(y-{{x}_{1}})}^{2}}=x_{1}^{2}\]                    Þ \[{{x}^{2}}+{{y}^{2}}-2{{x}_{1}}(x+y)+x_{1}^{2}=0\].


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