JEE Main & Advanced Mathematics Circle and System of Circles Question Bank System of circles

  • question_answer
    If the two circles \[2{{x}^{2}}+2{{y}^{2}}-3x+6y+k=0\] and \[{{x}^{2}}+{{y}^{2}}-4x+10y+16=0\] cut orthogonally, then the value of k is [Kerala (Engg.) 2002]

    A)            41  

    B)            14

    C)            4    

    D)            0

    Correct Answer: C

    Solution :

               Given circles are                                     \[2{{x}^{2}}+2{{y}^{2}}-3x+6y+k=0\]                    or \[{{x}^{2}}+{{y}^{2}}-\frac{3}{2}x+3y+\frac{k}{2}=0\]                              .....(i)                    and \[{{x}^{2}}+{{y}^{2}}-4x+10y+16=0\]           .....(ii)                    Circle (i) and (ii) cut orthogonally, then \[2{{g}_{1}}\,{{g}_{2}}+2{{f}_{1}}{{f}_{2}}={{c}_{1}}+{{c}_{2}}\]                    \[2\text{ }\left( -\frac{3}{4} \right)\,(-2)+2\text{ }\left( \frac{3}{2} \right)\,.\,5=\frac{k}{2}+16\]                    \[3+15=\frac{k}{2}+16\]Þ \[18=\frac{k}{2}+16\]Þ \[k=4.\]


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