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

  • question_answer
    The locus of a point which moves such that the sum of the squares of its distances from the three vertices of a triangle is constant, is a circle whose centre is at the

    A)            Incentre of the triangle            

    B)            Centroid of the triangle

    C)            Orthocentre of the triangle

    D)            None of these

    Correct Answer: B

    Solution :

               Let a triangle has its three vertices as (0, 0), (a, 0), (0, b). We have the moving point (h, k) such that \[{{h}^{2}}+{{k}^{2}}+{{(h-a)}^{2}}+{{k}^{2}}+{{h}^{2}}+{{(k-b)}^{2}}=c\]                    \[\Rightarrow 3{{h}^{2}}+3{{k}^{2}}-2ah-2bk+{{a}^{2}}+{{b}^{2}}=c\]                    Therefore, \[3{{x}^{2}}+3{{y}^{2}}-2ax-2by+{{a}^{2}}+{{b}^{2}}=c\]                    Its centre is \[\left( \frac{a}{3},\ \frac{b}{3} \right)\], which is centroid of \[\Delta \].


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