CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    If\[\omega \]is a complex cube root of unity, then the value of\[\sin \left\{ ({{\omega }^{10}}+{{\omega }^{23}})\pi -\frac{\pi }{6} \right\}\]is

    A)  \[\frac{1}{\sqrt{2}}\]                    

    B)         \[\frac{\sqrt{3}}{2}\]

    C)  \[-\frac{1}{\sqrt{2}}\]   

    D)         \[-\frac{\sqrt{3}}{2}\]

    E)  \[\frac{1}{2}\]

    Correct Answer: E

    Solution :

    Since, \[\omega \] is a complex cube root of unity. \[\therefore \]\[{{\omega }^{10}}+{{\omega }^{23}}={{({{\omega }^{3}})}^{3}}\omega +{{({{\omega }^{3}})}^{7}}{{\omega }^{2}}\] \[=\omega +{{\omega }^{2}}=-1\] \[\therefore \]  \[\sin \left\{ ({{\omega }^{10}}+{{\omega }^{23}})\pi -\frac{\pi }{6} \right\}\]                                 \[=\sin \left( -\pi -\frac{\pi }{6} \right)=-\sin \left( \pi +\frac{\pi }{6} \right)\]                 \[=\sin \frac{\pi }{6}=\frac{1}{2}\]


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