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

  • question_answer
    The point of contact of the given circles \[{{x}^{2}}+{{y}^{2}}-6x-6y+10=0\] and \[{{x}^{2}}+{{y}^{2}}=2\], is 

    A)            (0, 0)                                         

    B)            (1, 1)

    C)            (1, -1)                                       

    D)            (-1, -1)

    Correct Answer: B

    Solution :

               \[{{x}^{2}}+{{y}^{2}}-6x-6y+10=0\]               ?. (i)                    \[{{x}^{2}}+{{y}^{2}}=2\]                                           ?. (ii)                    \[\Rightarrow -6x-6y+12=0\] or \[x+y-2=0\]     ?. (iii)                    \[\Rightarrow {{x}^{2}}+{{y}^{2}}+2xy=4\]                                        {from (iii)}                    or \[2xy=2\]                                    {from (ii)}                    and \[x-y=\sqrt{{{(x+y)}^{2}}-4xy}=\sqrt{4-4}=0\]                    or \[x=y\] and \[x+y=2\]\[\Rightarrow x=1,\ y=1\].                    Trick: Required point must satisfy both the circles. Obviously (1, 1) satisfies both the equations simultaneously.


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