RAJASTHAN ­ PET Rajasthan PET Solved Paper-2004

  • question_answer
    Equation of radical axis of the circles \[{{x}^{2}}+{{y}^{2}}+4x+7=0\]and\[2{{x}^{2}}+2{{y}^{2}}+3x+5y+9=0\]is

    A)  \[x+y+1=0\]      

    B)  \[x+y-1=0\]

    C)  \[x-y-1=0\]      

    D)  \[x-y+1=0\]

    Correct Answer: D

    Solution :

     Given, equation of circles are \[{{S}_{1}}\equiv {{x}^{2}}+{{y}^{2}}+4x+7=0\] and \[{{S}_{2}}\equiv 2{{x}^{2}}+2{{y}^{2}}+3x+5y+9=0\] or \[{{S}_{2}}\equiv {{x}^{2}}+{{y}^{2}}+\frac{3}{2}x+\frac{5}{2}y+\frac{9}{2}=0\] Equation of radical axis\[{{S}_{1}}-{{S}_{2}}=0\] \[\Rightarrow \] \[({{x}^{2}}+{{y}^{2}}+4x+7)\]           \[-\left( {{x}^{2}}+{{y}^{2}}+\frac{3}{2}x+\frac{5}{2}y+\frac{9}{2} \right)=0\] \[\Rightarrow \] \[\left( 4-\frac{3}{2} \right)x-\frac{5}{2}y+7-\frac{9}{2}=0\] \[\Rightarrow \] \[\frac{5}{2}x-\frac{5}{2}y+7-\frac{9}{2}=0\] \[\Rightarrow \] \[x-y+1=0\]


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