JEE Main & Advanced JEE Main Paper (Held On 19 May 2012)

  • question_answer
    If three distinct points A, B, C are given in the 2- dimensional coordinate plane such that the ratio of the distance of each one of them from the point (1, 0) to the distance from (- 1,0) is equal to \[\frac{1}{2},\]then the circum centre of the triangle ABC is at, the point.     JEE Main  Online Paper (Held On 19  May  2012)

    A) \[\left( \frac{5}{3},0 \right)\]         

    B)                        (0,0)

    C)                        \[\left( \frac{1}{3},0 \right)\]                     

    D)                        (3,0)

    Correct Answer: A

    Solution :

                    Let\[P(1,0)\]and\[Q(-1,0),A(x,y)\] Given:\[\frac{AP}{AQ}=\frac{BP}{BQ}=\frac{CP}{CQ}=\frac{1}{2}\] \[\Rightarrow \]\[2AP=AQ\]\[\Rightarrow \]\[4{{(AP)}^{2}}=A{{Q}^{2}}\] \[\Rightarrow \]\[4[{{(x-1)}^{2}}+{{y}^{2}}]={{(x+1)}^{2}}+{{y}^{2}}\] \[\Rightarrow \]\[4({{x}^{2}}+1-2x)+4{{y}^{2}}={{x}^{2}}+1+2x+{{y}^{2}}\] \[\Rightarrow \]\[3{{x}^{2}}+3{{y}^{2}}-8x-2x+4-1=0\] \[\Rightarrow \]\[3{{x}^{2}}+3{{y}^{2}}-10x+3=0\] \[\Rightarrow \]\[{{x}^{2}}+{{y}^{2}}-\frac{10}{3}x+1=0\]                                             ?(1) \[\therefore \]A lies on the circle given by (1). As B and C also follow the same condition. \[\therefore \]Centre of circumcircle of \[\Delta ABC=\]centre of circle given by (1)\[=\left( \frac{5}{3},0 \right)\]                


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