CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2008

  • question_answer
    If a is a complex number satisfying the equation \[{{a}^{2}}+a+1=0,\]then \[{{\alpha }^{31}}\]is equal to

    A)  \[\alpha \]                                         

    B)  \[{{\alpha }^{2}}\]

    C)  \[1\]                                    

    D)  \[i\]

    Correct Answer: A

    Solution :

    Given equation is \[{{\alpha }^{2}}+\alpha +1=0\]                 \[\therefore \]\[\alpha =\frac{-1\pm \sqrt{1-4}}{2}=\frac{-1\pm \sqrt{3}i}{2}\] Let it be   \[\alpha =\omega ,\,{{\omega }^{2}}\] (1) If      \[\alpha =\omega ,\,\] then \[{{\alpha }^{31}}={{(\omega )}^{31}}=\omega =\alpha \] (2) If  \[\alpha ={{\omega }^{2}},\] then \[{{\alpha }^{31}}={{({{\omega }^{2}})}^{31}}={{\omega }^{62}}={{\omega }^{2}}=\alpha \] Hence, \[{{\alpha }^{31}}\] is equal to a.


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