10th Class Mathematics Quadratic Equations Question Bank Quadratic Equations

  • question_answer
    For what value of a, the roots of the equation \[2{{x}^{2}}+6x+a=0,\]satisfy the condition \[\left( \frac{\alpha }{\beta } \right)+\left( \frac{\beta }{\alpha } \right)<2\] (where \[\alpha \] and \[\beta \]are the roots of equation).

    A)  \[a<0\]                      

    B)                     \[-1<a<0\]    

    C)                     \[-1<a<1\]                

    D)                     None of these 

    Correct Answer: D

    Solution :

    Given equation is \[2{{x}^{2}}+6x+a=0\] Now,   \[\left( \frac{\alpha }{\beta } \right)+\left( \frac{\beta }{\alpha } \right)<2\] \[\Rightarrow \] \[\frac{{{\alpha }^{2}}+{{\beta }^{2}}}{\alpha \beta }<2\]  \[\Rightarrow \] \[\frac{{{(\alpha +\beta )}^{2}}-2\alpha \beta }{\alpha \beta }<2\] \[\Rightarrow \] \[\frac{9-a}{a/2}<2\]\[\Rightarrow \] \[9-a<a\] \[\left[ \begin{align}   & \because \,\,\,\alpha +\beta =-3 \\  & and\,\,\alpha \beta =\frac{a}{2} \\ \end{align} \right]\] \[\Rightarrow \] \[\frac{9}{2}<a\]


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