JEE Main & Advanced Sample Paper JEE Main - Mock Test - 12

  • question_answer
    If \[\alpha \] and \[\beta \] are the roots of \[2{{x}^{2}}+7x+c=0\]and\[|{{\alpha }^{2}}-{{\beta }^{2}}|=\frac{7}{4}\]then c is equal to

    A) 2                     

    B) 3         

    C) 6                     

    D) 5

    Correct Answer: C

    Solution :

    \[|{{\alpha }^{2}}-{{\beta }^{2}}=\,\,|(\alpha +\beta )|\,\,\,|\alpha -\beta |\]
    \[\Rightarrow \,\,\,\frac{7}{4}=|\alpha -\beta |.\frac{7}{2}\]
    \[\Rightarrow \,\,\,|\alpha -\beta {{|}^{2}}=\frac{1}{4}\,\,\,\Rightarrow \,\,\,|{{(\alpha +\beta )}^{2}}-4\alpha \beta |=\frac{1}{4}\]
    \[\Rightarrow \,\,\left| \frac{49}{4}-\frac{4c}{2} \right|=\frac{1}{4}\]
    \[\Rightarrow \,\,49-8c=1\Rightarrow \,c=\frac{48}{8}=6\]


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