JEE Main & Advanced Mathematics Circle and System of Circles Question Bank System of circles

  • question_answer
    The points of intersection of circles \[{{x}^{2}}+{{y}^{2}}=2ax\] and \[{{x}^{2}}+{{y}^{2}}=2by\] are                                                   [AMU 2000]

    A)            (0, 0), (a, b)                              

    B)            (0, 0), \[\left( \frac{2a{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}},\frac{2b{{a}^{2}}}{{{a}^{2}}+{{b}^{2}}} \right)\]

    C)            (0, 0), \[\left( \frac{{{a}^{2}}+{{b}^{2}}}{{{a}^{2}}},\frac{{{a}^{2}}+{{b}^{2}}}{{{b}^{2}}} \right)\]

    D)  None of the above                            

    Correct Answer: B

    Solution :

               Given circles are \[{{x}^{2}}+{{y}^{2}}=2ax\]                            ?..(i)                     and \[{{x}^{2}}+{{y}^{2}}=2by\]                                                             ?..(ii)                        (i) ? (ii) Þ \[0=2(ax-by)\] Þ \[y=\frac{a}{b}x\]                    From (i), \[{{x}^{2}}+\frac{{{a}^{2}}}{{{b}^{2}}}{{x}^{2}}=2ax\] Þ \[x\left\{ \left( 1+\frac{{{a}^{2}}}{{{b}^{2}}} \right)x-2a \right\}=0\]                    Þ \[x=0,\ \frac{2a{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}}\]                    For \[x=0\], \[y=0\] and for \[x=\frac{2a{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}}\], \[y=\frac{2{{a}^{2}}b}{{{a}^{2}}+{{b}^{2}}}\]                    \ The points of intersection are (0, 0) and \[\left( \frac{2a{{b}^{2}}}{{{a}^{2}}+{{b}^{2}}},\ \frac{2{{a}^{2}}b}{{{a}^{2}}+{{b}^{2}}} \right)\].


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