JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2008

  • question_answer
        The equation of the common tangent of the two touching circles,\[{{y}^{2}}+{{x}^{2}}-6x-12y+37=0\]and\[{{x}^{2}}+{{y}^{2}}-6y+7=0\]is

    A)  \[x-y-5=0\]       

    B)  \[x-y+5=0\]

    C)  \[x-y-5=0\]

    D)  \[x+y+5=0\]

    Correct Answer: C

    Solution :

                    Let    \[{{S}_{1}}\equiv {{x}^{2}}+{{y}^{2}}-6x-12y+37=0\] and   \[{{S}_{2}}\equiv {{x}^{2}}+{{y}^{2}}-6y+7=0\] The equation of common tangent of the two circles is\[{{S}_{2}}-{{S}_{2}}=0\] \[\Rightarrow \]               \[{{x}^{2}}+{{y}^{2}}-6x-12y+37\]                 \[-({{x}^{2}}+{{y}^{2}}-6y+7)=0\] \[\Rightarrow \]               \[-6x+6y+30=0\] \[\Rightarrow \]               \[x-y-5=0\]        


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