CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2009

  • question_answer
    If \[\alpha \] and \[\beta \] are the roots of  then \[{{\alpha }^{16}}+{{\beta }^{16}}\] is equal to

    A)  \[1\]                                    

    B)  \[-1\]

    C)  \[2\]                                    

    D)  \[0\]

    Correct Answer: B

    Solution :

    Given, equation is \[{{x}^{2}}+x+1=0\] \[\Rightarrow \]               \[x=\frac{-1\pm \sqrt{3}i}{2}\] \[\Rightarrow \]               \[x=\omega ,\,{{\omega }^{2}}\] Since, \[\alpha \] and \[\beta \] are the roots of \[{{x}^{2}}+x+1=0\] \[\therefore \]  \[\alpha =\omega \] and \[\beta ={{\omega }^{2}}\] Now,    \[{{\alpha }^{16}}+{{\beta }^{16}}={{(\omega )}^{16}}+{{({{\omega }^{2}})}^{16}}\]                 \[={{\omega }^{16}}+{{\omega }^{22}}\]                 \[=\omega +{{\omega }^{2}}\]  \[(\because \,{{\omega }^{3}}=1)\]                 \[=-1\]                  \[(\because \,\,1+\omega +{{\omega }^{2}}=0)\]


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