BCECE Engineering BCECE Engineering Solved Paper-2006

  • question_answer
    If the circle \[{{x}^{2}}+{{y}^{2}}+4x+22y+c=0\]bisects  the circumference of the circle \[{{x}^{2}}+{{y}^{2}}-2x+8y-d=0,\] then \[c+d\]is equal to :

    A)  60                         

    B)         50                         

    C)  40                         

    D)         30

    Correct Answer: B

    Solution :

    Given that, circle \[{{x}^{2}}+{{y}^{2}}+4x+22y+c=0\] bisects the circumference of the circle                 \[{{x}^{2}}+{{y}^{2}}-2x+8y-d=0\] \[\therefore \] The common chord of the given circle is \[{{S}_{1}}-{{S}_{2}}=0\]                 \[\Rightarrow \]               \[{{x}^{2}}+{{y}^{2}}+4x+22y+c-{{x}^{2}}-{{y}^{2}}\]                                                 \[+\,2x-8y+d=0\]                 \[6x+14y+c+d=0\]                           ?(i) So, Eq. (i) passes through the centre of the second circle i.e., \[(1,-4)\]                 \[\therefore \]  \[6-56+c+d=0\]                 \[\Rightarrow \]               \[c+d=50\] Note: If \[{{S}_{1}}\]and \[{{S}_{2}}\] are the equations of two circles, then equation of common chord is \[{{S}_{1}}-{{S}_{2}}=0.\]


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