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

  • question_answer
    The value of \[\lambda \], for which the circle \[{{x}^{2}}+{{y}^{2}}+2\lambda x+6y+1=0\], intersects the circle \[{{x}^{2}}+{{y}^{2}}+4x+2y=0\]orthogonally is [MP PET 2004]

    A)            \[\frac{-5}{2}\]                        

    B)            \[-1\]

    C)            \[\frac{-11}{8}\]                      

    D)            \[\frac{-5}{4}\]

    Correct Answer: D

    Solution :

               If two circles \[{{x}^{2}}+{{y}^{2}}+2{{g}_{1}}x+2{{f}_{1}}y+{{c}_{1}}=0\] and \[2({{g}_{1}}{{g}_{2}}+{{f}_{1}}{{f}_{2}})={{c}_{1}}+{{c}_{2}}\] intersect orthogonally then they must follow                    \[2({{g}_{1}}{{g}_{2}}+{{f}_{1}}{{f}_{2}})={{c}_{1}}+{{c}_{2}}\] and \[{{g}_{1}}=\lambda ,\,{{f}_{1}}=3,\,{{c}_{1}}=1\]                    and \[{{g}_{2}}=2,\,{{f}_{2}}=1,\,{{c}_{2}}=0\]                    So, \[2\,(2\lambda +3)=1+0\Rightarrow 2\lambda +3=\frac{1}{2}\] \[\Rightarrow \lambda =\frac{-5}{4}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner