CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2007

  • question_answer
    If \[1,\,\omega ,\,{{\omega }^{2}}\] are the cube roots of unity then \[(1+\omega )(1+{{\omega }^{2}})(1+{{\omega }^{4}})(1+{{\omega }^{8}})\]is equal to

    A)  \[1\]                                    

    B)  \[0\]

    C)  \[{{\omega }^{2}}\]                                       

    D)  \[\omega \]

    Correct Answer: A

    Solution :

    Given, \[(1+\omega )\,(1+{{\omega }^{2}})(1+{{\omega }^{4}})(1+{{\omega }^{8}})\] \[=(1+\omega )(-\omega )\{1+{{\omega }^{2}}.\omega )(1+{{({{\omega }^{2}})}^{2}}.{{\omega }^{2}}\}\]                                 \[[\because \,\,1+\omega +{{\omega }^{2}}=0]\] \[=(1+\omega )(-\omega )(1+\omega )(1+{{\omega }^{2}})\]     \[[\because \,{{\omega }^{3}}=1]\] \[={{(1+\omega )}^{2}}(-\omega -{{\omega }^{3}})\] \[=(1+{{\omega }^{2}}+2\omega )(-\omega -{{\omega }^{3}})\] \[=(1+{{\omega }^{2}}+2\omega )(-\omega -1)\] \[=(-\omega +2\omega )(+{{\omega }^{2}})={{\omega }^{3}}=1\]


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