J & K CET Engineering J and K - CET Engineering Solved Paper-2004

  • question_answer
    For the equation \[\frac{1}{x+a}-\frac{1}{x+b}=\frac{1}{x+c},\]if the product of the ratio is zero, then the sum of (he roots is

    A)  \[0\]

    B)  \[\frac{2ab}{b+c}\]

    C)  \[\frac{2ac}{b+c}\]

    D)  \[-\frac{2ac}{b+c}\]

    Correct Answer: D

    Solution :

    Given equation can be rewritten as \[\frac{b-a}{{{x}^{2}}+(a+b)x+ab}=\frac{1}{x+c}\] \[\Rightarrow \] \[{{x}^{2}}+(a+b)x+ab=(b-a)x+(b-a)c\] \[\Rightarrow \] \[{{x}^{2}}+2ax+ab+ca-bc=0\] Since, the product of roots is zero. \[\therefore \] \[ab+ca-bc=0\] \[\Rightarrow \] \[a(b+c)=bc\] \[\Rightarrow \] \[a=\frac{bc}{b+c}\] \[\therefore \]  Sum of roots \[=-2a=\frac{-2bc}{b+c}\]


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