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

  • question_answer
    If a circle passes through the point (0, 0), (a, 0), (0, b), then its centre is                                        [MNR 1975]

    A)            \[(a,\ b)\]                                   

    B)            \[(b,\ a)\]

    C)            \[\left( \frac{a}{2},\ \frac{b}{2} \right)\]                                    

    D)            \[\left( \frac{b}{2},\ -\frac{a}{2} \right)\]

    Correct Answer: C

    Solution :

     Let the equation of circle be \[{{x}^{2}}+{{y}^{2}}+2gx+2fy+c=0\]. Now on passing through the points, we get three equations.                   \[c=0\]                                                                ?.(i)                    \[{{a}^{2}}+2ga+c=0\]                                                 ?.(ii)                    \[{{b}^{2}}+2fb+c=0\]                                                 ?.(iii)                        On solving them, we get \[g=-\frac{a}{2},\ f=-\frac{b}{2}\]                    Hence the centre is\[\left( \frac{a}{2},\ \frac{b}{2} \right)\].


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