JCECE Engineering JCECE Engineering Solved Paper-2004

  • question_answer
    If\[\alpha ,\,\,\beta ,\,\,\gamma \]are the roots of the equation\[{{x}^{3}}+4x+1=0\]then\[{{(\alpha +\beta )}^{-1}}+{{(\beta +\gamma )}^{-1}}+{{(\gamma +\alpha )}^{-1}}\]is equal to:

    A) \[2\]                                     

    B) \[3\]

    C) \[4\]                                     

    D) \[5\]

    Correct Answer: C

    Solution :

    Since, \[\alpha ,\,\,\beta ,\,\,\gamma \] are the roots of the equation\[{{x}^{3}}+4x+1=0\], then \[\alpha +\beta +\gamma =0,\,\,\alpha \beta +\beta \gamma +\gamma \alpha =4\]and\[\alpha \beta \gamma =-1\] \[\therefore \]  \[\frac{1}{\alpha +\beta }+\frac{1}{\beta +\gamma }+\frac{1}{\gamma +\alpha }=-\frac{1}{\gamma }-\frac{1}{\alpha }-\frac{1}{\beta }\]                 \[(\because \,\,\alpha +\beta +\gamma =0)\]


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