KVPY Sample Paper KVPY Stream-SX Model Paper-27

  • question_answer
    If \[\alpha \] and \[\beta \] are the roots of the equation \[a{{x}^{2}}+bx+c=0,\]\[(a,b,c\in \mathbf{R})\] then\[(1+\alpha +{{\alpha }^{2}})\,\,(1+\beta +{{\beta }^{2}}),\] is -

    A) < 0      

    B) > 0

    C) = 0

    D) None of these

    Correct Answer: B

    Solution :

    \[\alpha +\beta =-\,b/a\] & \[\alpha \beta =c/a\] Then \[(1+\alpha +{{\alpha }^{2}})\,\,(1+\beta +{{\beta }^{2}})\]
    \[=1+(\alpha +\beta )+(\alpha \beta )+{{(\alpha \beta )}^{2}}+({{\alpha }^{2}}+{{\beta }^{2}})+\alpha \beta (\alpha +\beta )\]\[=1-\frac{b}{a}+\frac{c}{a}+\frac{{{c}^{2}}}{{{a}^{2}}}+\frac{{{b}^{2}}}{{{a}^{2}}}-\frac{2c}{a}-\frac{bc}{{{a}^{2}}}\]
    \[=\frac{{{a}^{2}}+ab+ac+{{c}^{2}}+{{b}^{2}}-2ac-bc}{{{a}^{2}}}\]
    \[=\frac{{{a}^{2}}+{{b}^{2}}+{{c}^{2}}-ab-bc-ac}{{{a}^{2}}}\]
    \[=\frac{(2{{a}^{2}}+2{{b}^{2}}+2{{c}^{2}}-2ab-2bc-2ac)}{2{{a}^{2}}}\]
    \[=\frac{{{(a-b)}^{2}}+{{(b-c)}^{2}}+{{(a-c)}^{2}}}{2{{a}^{2}}}>0\]


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