RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    If area of the circle\[4{{x}^{2}}+4{{y}^{2}}-8x+16y+k=0\]is\[9\pi \]sq units, then the value of k is

    A)  4              

    B)  \[10\]

    C)  \[-16\]            

    D)  ±16

    Correct Answer: C

    Solution :

     Equation of circle is \[4{{x}^{2}}+4{{y}^{2}}-8x+16y+k=0\] \[\therefore \] Radius of circle \[\sqrt{1+4-\frac{k}{4}}=\sqrt{5-\frac{k}{4}}\] According to the question, area of circle \[\pi {{r}^{2}}=9\pi \] \[\Rightarrow \] \[\pi \left( 5-\frac{k}{4} \right)=9\pi \] \[\Rightarrow \] \[5-\frac{k}{4}=9\] \[\Rightarrow \] \[\frac{k}{4}=-4\] \[\Rightarrow \] \[k=-16\]


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