JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank De Moivre's theorem and Roots of unity

  • question_answer
    \[{{\left( -\frac{1}{2}+\frac{\sqrt{3}}{2}i \right)}^{1000}}=\]

    A) \[\frac{1}{2}+\frac{\sqrt{3}}{2}i\]

    B) \[\frac{1}{2}-\frac{\sqrt{3}}{2}i\]

    C) \[-\frac{1}{2}+\frac{\sqrt{3}}{2}i\]

    D) None of these

    Correct Answer: C

    Solution :

    Here  \[-\frac{1}{2}+\frac{1}{2}i\sqrt{3}\] is one of the two imaginary cube root of unity. If we denote it by\[\omega \]. Then\[{{\omega }^{1000}}={{\omega }^{999}}\omega ={{({{\omega }^{3}})}^{333}}\omega =\omega =-\frac{1}{2}+\frac{\sqrt{3}}{2}i\].


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