JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Self Evaluation Test - Complex Numbers and Quadratic Equations

  • question_answer
    If \[\alpha ,\beta \] are roots of \[a{{x}^{2}}+bx+b=0,\] then \[\sqrt{\frac{\alpha }{\beta }}+\sqrt{\frac{\beta }{\alpha }}+\sqrt{\frac{b}{a}}\] is (\[{{b}^{2}}\ge 4ab,\] a and b are of same sign)

    A) 0         

    B) 1   

    C) 2                     

    D) \[2\sqrt{\frac{b}{a}}\]

    Correct Answer: D

    Solution :

    \[{{\left( \sqrt{\frac{\alpha }{\beta }}+\sqrt{\frac{\beta }{\alpha }} \right)}^{2}}=\frac{{{\alpha }^{2}}+{{\beta }^{2}}}{\alpha \beta }+2=\frac{{{(\alpha +\beta )}^{2}}}{\alpha \beta }\] \[=\frac{{{\left( -\frac{b}{a} \right)}^{2}}}{\left( \frac{b}{a} \right)}=\frac{b}{a}\] \[\therefore \,\,\sqrt{\frac{\alpha }{\beta }}+\sqrt{\frac{\beta }{\alpha }}=\sqrt{\frac{b}{a}}\]       [\[\because \,\,\alpha ,\beta \] are real] \[\sqrt{\frac{\alpha }{\beta }}+\sqrt{\frac{\beta }{\alpha }}+\sqrt{\frac{b}{a}}=2\sqrt{\frac{b}{a}}\]


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