CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2002

  • question_answer
    If\[\omega \] is a non-real cube root of unity, then\[(a+b)(a+b\omega )(a+b{{\omega }^{2}})\] is equal to:

    A)  \[{{a}^{3}}+{{b}^{3}}\] 

    B)                                         \[{{a}^{3}}-{{b}^{3}}\]

    C)                         \[{{a}^{2}}+{{b}^{2}}\]                 

    D)                         \[{{a}^{2}}-{{b}^{2}}\]

    E)                         0

    Correct Answer: B

    Solution :

    \[(a+b)(a+b\omega )(a+b{{\omega }^{2}})\] \[=(a+b)[{{a}^{2}}+ab(\omega +{{\omega }^{2}})+{{b}^{2}}{{\omega }^{3}}]\] \[=(a+b)({{a}^{2}}-ab+{{b}^{2}})\] \[={{a}^{3}}-{{b}^{3}}\]


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