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 which passes through the points (2, 3) and (4, 5) and the centre lies on the straight line \[y-4x+3=0\], is [RPET 1985; MP PET 1989]

    A)            \[{{x}^{2}}+{{y}^{2}}+4x-10y+25=0\]

    B)            \[{{x}^{2}}+{{y}^{2}}-4x-10y+25=0\]

    C)            \[{{x}^{2}}+{{y}^{2}}-4x-10y+16=0\]

    D)            \[{{x}^{2}}+{{y}^{2}}-14y+8=0\]

    Correct Answer: B

    Solution :

               First find the centre. Let centre be (h, k), then                    \[\sqrt{{{(h-2)}^{2}}+{{(k-3)}^{2}}}=\sqrt{{{(h-4)}^{2}}+{{(k-5)}^{2}}}\]                ?.(i)                    and \[k-4h+3=0\]                                          ?.(ii)                    From (i), we get \[-4h-6k+8h+10k=16+25-4-9\]                    or \[4h+4k-28=0\] or \[h+k-7=0\]          ?.(iii)                    From (iii) and (ii), we get (h, k) as (2, 5). Hence centre is   (2, 5) and radius is 2. Now find the equation of circle.                      Trick : Obviously, circle \[{{x}^{2}}+{{y}^{2}}-4x-10y+25=0\] passes through (2, 3) and (4, 5).


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