JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Chord of contact of tangent, Pole and Polar

  • question_answer
    From the origin chords are drawn to the circle\[{{(x-1)}^{2}}+{{y}^{2}}=1\]. The equation of the locus of the middle points of these chords is [IIT 1985; EAMCET 1991]

    A)            \[{{x}^{2}}+{{y}^{2}}-3x=0\]                                          

    B)            \[{{x}^{2}}+{{y}^{2}}-3y=0\]

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

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

    Correct Answer: C

    Solution :

               The given circle is\[{{x}^{2}}+{{y}^{2}}-2x=0\]. Let \[({{x}_{1}},\ {{y}_{1}})\] be the middle point of any chord of this circle, than its equation is \[{{S}_{1}}=T\].                    or \[x_{1}^{2}+y_{1}^{2}-2{{x}_{1}}=x{{x}_{1}}+y{{y}_{1}}-(x+{{x}_{1}})\]                    If it passes through (0, 0), then                      \[x_{1}^{2}+y_{1}^{2}-2{{x}_{1}}=-{{x}_{1}}\Rightarrow x_{1}^{2}+y_{1}^{2}-{{x}_{1}}=0\]                    Hence the required locus of the given point \[({{x}_{1}},\ {{y}_{1}})\] is \[{{x}^{2}}+{{y}^{2}}-x=0\].


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