Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    Let\[a,\,\,b,\,\,c\]be real numbers with\[a\ne 0\]and let \[\alpha ,\,\,\beta \]be the roots of the equation\[a{{x}^{2}}+bx+c=0\], then\[{{a}^{3}}{{x}^{2}}+abcx+{{c}^{3}}=0\]has roots

    A) \[{{\alpha }^{2}}\beta ,{{\beta }^{2}}\alpha \]                    

    B) \[\alpha ,{{\beta }^{2}}\]

    C) \[{{\alpha }^{2}}\beta ,\beta \alpha \]   

    D)        \[{{\alpha }^{3}}\beta ,{{\beta }^{3}}\alpha \]

    Correct Answer: A

    Solution :

    Dividing the equation \[{{a}^{3}}{{x}^{2}}+abcx+{{c}^{3}}=0\]by\[{{c}^{2}}\], we get                 \[a{{\left( \frac{ax}{c} \right)}^{2}}+b\left( \frac{ax}{c} \right)+c=0\] \[\Rightarrow \]               \[\frac{ax}{c}=\alpha ,\,\,\beta \]are roots. \[\Rightarrow \]               \[x=\frac{c}{a}\alpha \]and\[x=\frac{c}{a}\beta \] \[\Rightarrow \]               \[x={{\alpha }^{2}}\beta \]and\[x=\alpha {{\beta }^{2}}\]                 [\[\because \,\,\alpha \beta =\frac{c}{a}\]as\[\alpha \],\[\beta \]are the roots of                                                 \[a{{x}^{2}}+bx+c=0\]] are roots of above equation.


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