JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    The radical centre of the circles                 \[{{x}^{2}}+{{y}^{2}}-16x+60=0\],                 \[{{x}^{2}}+{{y}^{2}}-12x+27=0\] and        \[{{x}^{2}}+{{y}^{2}}-12y+8=0\]is

    A) \[\left( 13,\,\,\frac{33}{4} \right)\]                          

    B) \[\left( \frac{33}{4},\,\,-13 \right)\]

    C) \[\left( \frac{33}{4},\,\,13 \right)\]                          

    D)  None of these

    Correct Answer: D

    Solution :

    Given, equation of the circles are                 \[{{S}_{1}}\equiv {{x}^{2}}+{{y}^{2}}-16x+60=0\]               ... (i)                 \[{{S}_{2}}\equiv {{x}^{2}}+{{y}^{2}}-12x+27=0\]               ... (ii) And        \[{{S}_{3}}\equiv {{x}^{2}}+{{y}^{2}}-12y+8=0\] ... (iii) The radical axis of circles (i) and (ii) is                 \[{{S}_{1}}-{{S}_{2}}=0\] \[\Rightarrow \]               \[({{x}^{2}}+{{y}^{2}}-16x+60)\]                                 \[-({{x}^{2}}+{{y}^{2}}-12x+27)=0\] \[\Rightarrow \]               \[-4x+33=0\] \[\Rightarrow \]               \[x=\frac{33}{4}\]                                                            ? (iv) The radical axis of circles (ii) and (iii) is                 \[{{S}_{2}}-{{S}_{3}}=0\] \[\Rightarrow \]               \[({{x}^{2}}+{{y}^{2}}-12x+27)\]                                 \[-({{x}^{2}}+{{y}^{2}}-12y+8)=0\] \[\Rightarrow \]               \[-12x+12y+19=0\]                          ? (v) On solving Eqs. (iv) and (v), wef get radical centre\[\left( \frac{33}{4},\,\,\frac{20}{3} \right)\].


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