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

  • question_answer
    The equation of the circle having centre \[(1,\ -2)\] and passing through the point of intersection of lines \[3x+y=14\], \[2x+5y=18\] is [MP PET 1990]

    A)            \[{{x}^{2}}+{{y}^{2}}-2x+4y-20=0\]

    B)            \[{{x}^{2}}+{{y}^{2}}-2x-4y-20=0\]

    C)            \[{{x}^{2}}+{{y}^{2}}+2x-4y-20=0\]

    D)            \[{{x}^{2}}+{{y}^{2}}+2x+4y-20=0\]

    Correct Answer: A

    Solution :

               The point of intersection of \[3x+y-14=0\] and \[2x+5y-18=0\] are                    \[x=\frac{-18+70}{15-2},\ y=\frac{-28+54}{13}\Rightarrow x=4,\ y=2\]                    i.e., point is (4, 2).                    Therefore radius is \[\sqrt{(9)+(16)}=5\] and equation is \[{{x}^{2}}+{{y}^{2}}-2x+4y-20=0\].                    Trick : The only circle is \[{{x}^{2}}+{{y}^{2}}-2x+4y-20=0\], whose centre is (1, ?2­).


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