JCECE Engineering JCECE Engineering Solved Paper-2010

  • question_answer
    If \[\alpha ,\,\,\beta \] are the roots of equation\[8{{x}^{2}}-3x+27=0\], then the value of\[{{\left( \frac{{{\alpha }^{2}}}{\beta } \right)}^{1/3}}+{{\left( \frac{{{\beta }^{2}}}{\alpha } \right)}^{1/3}}\]is

    A) \[\frac{1}{3}\]                                   

    B) \[\frac{1}{4}\]

    C) \[\frac{7}{2}\]                                   

    D) \[4\]

    Correct Answer: B

    Solution :

    Since, \[\alpha ,\,\,\beta \] are the roots of the equation                 \[8{{x}^{2}}-3x+27=0\] \[\therefore \]  \[\alpha +\beta =\left( -\frac{3}{8} \right)=\frac{3}{8}\]                 \[\alpha \beta =\frac{27}{8}={{\left( \frac{3}{2} \right)}^{3}}\] Now,     \[{{\left( \frac{{{\alpha }^{2}}}{\beta } \right)}^{1/3}}+{{\left( \frac{{{\beta }^{2}}}{\alpha } \right)}^{1/3}}\]                 \[=\frac{{{\alpha }^{2/3}}\cdot {{\alpha }^{1/3}}+{{\beta }^{2/3}}\cdot {{\beta }^{1/3}}}{{{(\alpha \beta )}^{1/3}}}\]                 \[=\frac{\alpha +\beta }{{{(\alpha \beta )}^{1/3}}}\]                 \[=\frac{\frac{3}{8}}{{{\left( \frac{27}{8} \right)}^{1/3}}}=\frac{3}{8}\cdot \frac{2}{3}=\frac{1}{4}\]


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