CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2003

  • question_answer
    If the circles \[{{x}^{2}}+{{y}^{2}}+2gx+2fy=0\] and\[{{x}^{2}}+{{y}^{2}}+2gx+2fy=0\] touch each other then :

    A)  \[ff=gg\]                            

    B)  \[fg=fg\]

    C)  \[{{(fg)}^{2}}={{(fg)}^{2}}\]       

    D)  \[fg=fg\]

    Correct Answer: D

    Solution :

    As both the circles pass through the origin and so they must have the same tangent at (0, 0). The general equation of tangent of the given circles are \[x{{x}_{1}}+y{{y}_{1}}+g\,(x+{{x}_{1}})+f\,(y+{{y}_{1}})\,=0\] \[x{{x}_{1}}+y{{y}_{1}}+g\,(x+{{x}_{1}})+f\,(y+{{y}_{1}})\,=0\] Substituting \[{{x}_{1}}=0\] and \[{{y}_{1}}=0\] we get \[gx+fy=0\Rightarrow gx+fy=0\] or            \[\frac{f}{g}=\frac{f}{g}\]   or      \[gf=gf\]


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