JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    If \[\alpha \] and \[\beta \] are the solutions of the quadratic equation \[a{{x}^{2}}+bx+c=0\] such that \[\beta ={{\alpha }^{1/3}}\], then:

    A) \[{{(ac)}^{1/3}}+{{(ab)}^{1/3}}+c=0\]

    B) \[{{({{a}^{3}}b)}^{1/4}}+{{(a{{b}^{3}})}^{1/4}}+c=0\]

    C) \[{{({{a}^{3}}c)}^{1/4}}+{{(a{{c}^{3}})}^{1/4}}+b=0\]

    D) \[{{({{a}^{4}}c)}^{1/3}}+{{(a{{c}^{4}})}^{1/3}}+b=0\]

    Correct Answer: C

    Solution :

    Since, \[\alpha \] and \[\beta \] are the roots of the equation\[a{{x}^{2}}+bx+c=0\]. \[\therefore \]  \[\alpha +\beta =-\frac{b}{a}\]and\[\alpha \beta =\frac{c}{a}\] \[\Rightarrow \]\[\alpha +{{\alpha }^{1/3}}=-\frac{b}{a}\]and\[\alpha \cdot {{\alpha }^{1/3}}=\frac{c}{a}\] \[(\because \,\,given\,\,\beta ={{\alpha }^{1/3}})\] \[\Rightarrow \]               \[\alpha ={{\left( \frac{c}{a} \right)}^{3/4}}\] \[\therefore \]  \[{{\left( \frac{c}{a} \right)}^{3/4}}+{{\left( \frac{c}{a} \right)}^{1/4}}=-\frac{b}{a}\] \[\Rightarrow \]               \[{{({{a}^{3}}c)}^{1/4}}+{{(a{{c}^{3}})}^{1/4}}+b=0\]


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