CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
    Two circles centred at \[(2,3)\] and \[(5,6)\] intersect each other. If the radii are equal, the equation of the common chord is

    A) \[x+y+1=0\]

    B) \[x-y+1=0\]

    C) \[x+y-8=0\]

    D) \[x-y-8=0\]

    Correct Answer: C

    Solution :

    Let the radius of both circles are ‘r’. Now, equation of circle with centre at \[(2,3)\] is                 \[{{S}_{1}}\equiv {{(x-2)}^{2}}+{{(y-3)}^{2}}={{r}^{2}}\]  …(i) and equation of circle with centre at \[(5,6)\] is                 \[{{S}_{2}}\equiv {{(x-5)}^{2}}+{{(y-6)}^{2}}={{r}^{2}}\]  ….(ii) Now, the equation common chord                 \[\equiv \] Radical axis of \[{{S}_{1}}\] and \[{{S}_{2}}=0\]                 \[\equiv ({{S}_{1}}-{{S}_{2}})=0\]                 \[\equiv [{{(x-2)}^{2}}]+[{{(y-3)}^{2}}]\]                                 \[-{{[(x-5)]}^{2}}-{{[(y-6)]}^{2}}=0\]                 \[\equiv {{x}^{2}}+{{y}^{2}}+4-4x+9-6x\]                 \[-{{x}^{2}}-{{y}^{2}}-25-36+10x+12y=0\]                 \[\equiv 6x+6y-48=0\] Common chord \[\equiv x+y-8=0\]


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