JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2007

  • question_answer
        If the lines\[2x+3y+1=0\]and\[3x-y-4=0\] lie along diameters of a circle of circumference\[10\pi ,\]then the equation of the circle is

    A)  \[{{x}^{2}}+{{y}^{2}}-2x+2y-23=0\]

    B)  \[{{x}^{2}}+{{y}^{2}}-2x-2y-23=0\]

    C)  \[{{x}^{2}}+{{y}^{2}}+2x+2y-23=0\]

    D)  \[{{x}^{2}}+{{y}^{2}}+2x-2y-23=0\]

    Correct Answer: A

    Solution :

                    The lines\[2x+3y+1=0\]and\[3x-y-4=0\]are diameters of circle. On solving these equations, we get \[x=1\]and\[y=-1\] Therefore the centre of circle is\[(1,-1)\] and circumference of circle\[=10\pi \] \[\Rightarrow \]               \[2\pi r=10\pi \] \[\Rightarrow \]               \[r=5\] \[\therefore \]Equation of circle is                 \[{{(x-{{x}_{1}})}^{2}}+{{(y-{{y}_{1}})}^{2}}={{r}^{2}}\] \[\Rightarrow \]               \[{{(x-1)}^{2}}+{{(y+1)}^{2}}={{5}^{2}}\] \[\Rightarrow \]               \[{{x}^{2}}+1-2x+{{y}^{2}}+2y+1=25\] \[\Rightarrow \]               \[{{x}^{2}}+{{y}^{2}}-2x+2y-23=0\]


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