RAJASTHAN ­ PET Rajasthan PET Solved Paper-2012

  • question_answer
    If\[\alpha \]and\[\beta \]are the roots of the equation \[a{{x}^{2}}+bx+c=0,\]then\[\frac{\alpha }{\alpha \beta +b}+\frac{\beta }{a\alpha +b}\]is equal to

    A)  \[\frac{2}{a}\]

    B)  \[\frac{2}{b}\]

    C)  \[\frac{2}{c}\]

    D)  \[\frac{-2}{a}\]

    Correct Answer: D

    Solution :

    Since,\[\alpha \]and\[\beta \]are the roots of the equation \[a{{x}^{2}}+bx+c=0\] \[\therefore \] \[a{{\alpha }^{2}}+b\alpha +c=0\] and        \[a{{\beta }^{2}}+b\beta +c=0\] \[\Rightarrow \] \[a{{\alpha }^{2}}+b\alpha =a{{\beta }^{2}}+b\beta =-c\] \[\therefore \] \[\frac{\alpha }{a\beta +b}+\frac{\beta }{a\alpha +b}+\frac{\alpha \beta }{a{{\beta }^{2}}+b\beta }+\frac{\alpha \beta }{a{{\alpha }^{2}}+b\alpha }\] \[=\frac{2\alpha \beta }{-c}=\frac{2}{-c}.\frac{c}{a}=-\frac{2}{a}\]


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