BCECE Engineering BCECE Engineering Solved Paper-2013

  • question_answer
    The    line   \[(x-2)\cos \beta +(y-2)\sin \theta =1\] touches a circle for all value of \[\theta ,\] then the equation of circle is

    A)  \[{{x}^{2}}+{{y}^{2}}-4x-4y+7=0\]

    B)  \[{{x}^{2}}+{{y}^{2}}+4x+4y+7=0\]

    C)  \[{{x}^{2}}+{{y}^{2}}-4x-4y-7=0\]

    D)  None of the above

    Correct Answer: A

    Solution :

    Give line is \[(x-2)\cos \theta +(y-2)\sin \theta =1\]                                 \[={{\cos }^{2}}\theta +{{\sin }^{2}}\theta \] On comparing we get, \[x-2\cos \theta \]                 ...(i) \[y-2=\sin \theta \]               ...(ii) and On squaring and then adding Eqs. (i) and (ii), we get \[{{(x-2)}^{2}}+{{(y-2)}^{2}}={{\cos }^{2}}\theta +{{\sin }^{2}}\theta \] \[\Rightarrow \]\[{{(x-2)}^{2}}+{{(y-2)}^{2}}=1\] \[\Rightarrow \]\[{{x}^{2}}+{{y}^{2}}-4x-4y+7=0\]


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